As a Catholic, I try to approach Scripture as it has been interpreted by the Church rather than try to interpret Scripture for myself.  I know that most of Catholics throughout history (at least the ones we know about) believed that the earth is a sphere.  I do not want to take a position different from that of great Catholic minds like St. Bede, St. Thomas Aquinas, and St. Robert Bellarmine.  These brilliant and holy men accepted St. Augustine's teaching that Scripture is silent about the shape of the earth. They believed it was a matter of science and that science shows that the earth is a sphere.  Their arguments for a spherical earth make sense to me, but I would be reluctant to disagree with such men even if I could not follow the arguments.

The idea that the earth is flat had a few supporters in the early centuries of the Church, but it disappeared for more than a thousand years.  Belief in flat earth was revived in recent times by Protestants interpreting Scripture for themselves without reference to Catholic tradition.  There is no reason for Catholics to accept this belief.

It's just my opinion, but I think that they are afraid. Afraid that trads will look stupid. It's normal for humans to care about what others think, but the more I look at the lives of the saints, the more I realize that they cared more about what God thinks, rather than being so concerned with human respect. And lets face it, trads are more than "a little out there" already. Why add to the nuttiness by believing in a flat earth?

It is legitimate to be concerned about how trads proclaiming that the earth is flat makes all trads look bad.  St. Augustine wrote this: 

``Usually, even a non-Christian knows something about the earth, the heavens, and the other elements of this world, about the motion and orbit of the stars and even their size and relative positions, about the predictable eclipses of the sun and moon, the cycles of the years and the seasons, about the kinds of animals, shrubs, stones, and so forth, and this knowledge he holds to as being certain from reason and experience. Now, it is a disgraceful and dangerous thing for an infidel to hear a Christian, presumably giving the meaning of Holy Scripture, talking nonsense on these topics; and we should take all means to prevent such an embarrassing situation, in which people show up vast ignorance in a Christian and laugh it to scorn. The shame is not so much that an ignorant individual is derided, but that people outside the household of faith think our sacred writers held such opinions, and, to the great loss of those for whose salvation we toil, the writers of our Scripture are criticized and rejected as unlearned men. If they find a Christian mistaken in a field which they themselves know well and hear him maintaining his foolish opinions about our books, how are they going to believe those books in matters concerning the resurrection of the dead, the hope of eternal life, and the kingdom of heaven, when they think their pages are full of falsehoods and on facts which they themselves have learnt from experience and the light of reason? Reckless and incompetent expounders of Holy Scripture bring untold trouble and sorrow on their wiser brethren when they are caught in one of their mischievous false opinions and are taken to task by those who are not bound by the authority of our sacred books. For then, to defend their utterly foolish and obviously untrue statements, they will try to call upon Holy Scripture for proof and even recite from memory many passages which they think support their position, although they understand neither what they say nor the things about which they make assertion. [1 Timothy 1.7]'' 

Concern for human respect is a problem when we place it above Catholic teaching.  When it comes to flat earth, people merely have a personal opinion that they are attached to.  They would do better to refrain from promoting it since St. Augustine calls such behaviour "a disgraceful and dangerous thing."

I personally do not accept the idea of flat earth because it is not compatible with Catholic history and tradition.  However, if there are people who are afraid that it makes us look stupid, they are following the teaching of St. Augustine.

For me the test came in the centuries when the Fathers, popes and theologians were fighting the Pythagorean heresies. Pythagoras, they say, was one of the first famous philosophers who said the Earth was a globe. In his book, Professor Martinez records many of these Pythagorean heresies condemned by the Church and a global Earth was NOT one of them. In other words, never once in history did the Church believe the Bible states tghe Earth is flat.

There also exists on Earth the science of Geodesy that can measure the bending of the Earth.

These are my two reasons why Catholics should not insist the Bible reveals a flat-Earth. They can believe what they want themselves, but to drag the Bible into it is what Protestants did and still do.

The book On Man and the Universe is a collection of excerpts from the works of Aristotle.  You might want to check anything you see there against a version with the entire text.  You are quoting from a section on Metaphysics.   Here it is online: http://classics.mit.edu/Aristotle/metaphysics.7.vii.html

"Substance is thought to belong most obviously to bodies; and so we say that not only animals and plants and their parts are substances, but also natural bodies such as fire and water and earth and everything of the sort, and all things that are either parts of these or composed of these (either of parts or of the whole bodies), e.g. the physical universe and its parts, stars and moon and sun. But whether these alone are substances, or there are also others, or only some of these, or others as well, or none of these but only some other things, are substances, must be considered. Some think the limits of body, i.e. surface, line, point, and unit, are substances, and more so than body or the solid.

"Further, some do not think there is anything substantial besides sensible things, but others think there are eternal substances which are more in number and more real; e.g. Plato posited two kinds of substance-the Forms and objects of mathematics-as well as a third kind, viz. the substance of sensible bodies. And Speusippus made still more kinds of substance, beginning with the One, and assuming principles for each kind of substance, one for numbers, another for spatial magnitudes, and then another for the soul; and by going on in this way he multiplies the kinds of substance. And some say Forms and numbers have the same nature, and the other things come after them-lines and planes-until we come to the substance of the material universe and to sensible bodies.

"Regarding these matters, then, we must inquire which of the common statements are right and which are not right, and what substances there are, and whether there are or are not any besides sensible substances, and how sensible substances exist, and whether there is a substance capable of separate existence (and if so why and how) or no such substance, apart from sensible substances; and we must first sketch the nature of substance.

You can also compare against St. Thomas's commentary for a Catholic perspective: https://archive.org/stream/AquinasCommentaryOnTheMetaphysics/Metaphysics-Aristotle-Comm-Aquinas_djvu.txt

1265.
Second, he describes the philosophers' opinions about those substances which are not evident.
He says that it seems to some philosophers that the limits of bodies are the substances of
things, i.e., that surface, line, point and unit are substances to a greater degree than a body or
solid. And those who held this opinion differed in their views; because some, the
Pythagoreans, thought that no limits of this kind are separate from sensible bodies, while
others thought that there are certain eternal beings which are separate from and more
numerous than sensible things and have being to a greater degree. I say "have being to a
greater degree," because they are incorruptible and immobile, whereas sensible bodies are
corruptible and mobile; and "more numerous," because while sensible bodies belong only to
one order, these separate beings belong to two, inasmuch as "Plato claimed that there are two
kinds of separate substances," or two orders of separate substances, namely, the separate
Forms or Ideas and the objects of mathematics; and he also posited a third order — the
substances of sensible bodies.

[/pre]

Only the other day a rocket was seen taking two astronauts up to a space station orbiting the Earth. In the news it showed a curved Earth as wiewed from that space station. They say in time anybody with the money will be able to spend some time up there. Let us start a collection for flat-Earthers to go see the Earth from space which they say is an ongoing hoax. Thast should sort out the problem.

Unfortunately, you can't see anything up there (watch 2mins beginning at 00:48):


https://youtu.be/UMtZV7NLxFY?start=48

The video isn't there.