Good question. I'd also like to know why so many of them accuse Catholics of idolatry, when they worship "Old Glory" (a piece of cloth) and have no qualms erecting nativity sets at Christmastime (which are as much statues as those of the saints are).

Human Nature and Aquinas’ Taxonomy of sɛҳuąƖ Sins
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The most obviously unnatural sin is “bestiality,” i.e., sɛҳuąƖ intercourse with animals – a sin which offers an affront to the human species. Next in seriousness is sodomy, which is an affront to the natural relationship between male and female.

In third place are unnatural coital relationships between men and women – for example, anal intercourse, coitus interruptus, or other contraceptive measures – all of which are sinful because they do not observe “the right manner of copulation.”  In his Summa contra gentiles, Aquinas compares such relationships to homicide: “After the sin of homicide whereby a human nature already in existence is destroyed, this type of sin appears to take next place, for by it the generation of human nature is precluded.” By taking measures to prevent a human life from emerging naturally, such non-procreative sex constitutes an action against the potential human soul that might result.

The least serious “unnatural” sɛҳuąƖ sin is masturbation, in which pleasure is intentionally sought in isolation from natural social relationships.  Aquinas is careful to distinguish this from “nocturnal pollution” or other unintentional emission of semen, which is not sinful. In our era, we would include pornography, as a means to excite prurient sɛҳuąƖity, as connected with this sin.

Incest, which is borderline “natural,” if it involves male-female intercourse, is nevertheless a grievous sin since it flouts the natural relationships proper to people connected by consanguinity or affinity.

As regards normal male-female relationships, the most serious sin is of course rape, in which sɛҳuąƖ sinfulness is compounded with a serious sin of injustice, forced intercourse with someone who is unwilling.

Next in seriousness is sacrilege, for example, intercourse with a nun or priest who has taken a vow of chastity.  Because of the vow, this sin involves a direct offense to God; and if it is accompanied by rape, the seriousness is compounded.

Less serious is adultery, which is consensual, but is combined with the sin of injustice, since at least one of the parties is joined lawfully to another in marriage.

Finally, Aquinas makes a distinction between two of the least serious sɛҳuąƖ sins – “seduction” and “fornication.” In making this distinction he is in part taking into account the customs in his era, in which (as also in our own time) a father at a wedding will “give away” the bride.  The legal code then favored marriage, on condition of parental consent and consent of the bride; in the absence of such consent, civil penalties for seduction were prescribed.

Fornication, i.e. what we call “consensual sex” is defined by Aquinas as intercourse with a woman who is not a virgin, and in which no external aggravating circuмstances are relevant – e.g., the use of force, or the use of contraceptives.  This act is sinful because it militates against the social welfare of possible progeny who might result – leading to the possibility of children without a father to aid them with moral and intellectual guidance into adulthood.
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Speaking as someone who once was a Protestant and now attempts to show family and friends that Paul states divorce and remarriage is just as wrong as sodomy, I can give you several reasons why they either celebrate it, condone it, or look the other way. I've literally had a family member tell me they knew what the Bible said about remarriage but God told them to marry this divorced person. They will respond  to the tune of "How can two people who are so in happy in love be wrong in God's eyes?" It would cause them to have to possibly be seen as an hardliner who does love as God commanded. They simply believe once you are saved you are always saved, unless of course you are gαy. They never knew when Jesus mentioned adultery he was referring to those in second marriages, I get that response more than any other but it doesn't matter because God wants me to be happy so its ok. Lastly they really have no clue about anything in the Bible except the end times are coming and if Jesus were here today he would be a proud flag waving neo-con.

The Baptist church I grew up in used to have the biggest youth group in my area. It was not uncommon to have 100 teenagers on a Wednesday night. Now almost 20 years later they are lucky to have 10, in that same age range, on a Sunday morning. I'm conflicted to whether or not that makes me happy. I guess I'm not, I mean its not as if these people started going to the Catholic church. Lastly I remember when I was a teenager, our youth pastors put us through a program called "True Love Waits." Now I couldn't tell you anything that was said during those weeks but if you had told me that sex before marriage, divorce and remarriage were as bad as sodomy and that I was putting my eternal life at stake for doing either then I would have remembered that, but to say those things would have been mean and to be seen as mean is the most grave sin of all in today's society.

Quote from: TNVOL

The Baptist church I grew up in used to have the biggest youth group in my area. It was not uncommon to have 100 teenagers on a Wednesday night. Now almost 20 years later they are lucky to have 10, in that same age range, on a Sunday morning. I'm conflicted to whether or not that makes me happy.

I think the only reason to be genuinely happy about this drop in the Baptist youth group would be if those 90 kids had abandoned error and were now assisting at the True Mass on Sundays.