Knee-length "shorts" were common in Catholics schools in the first part of the last century.  I'm honestly not seeing the problem with these.  It's almost like people merely hear the term "shorts" and get "triggered" by the word.

I’m not that bad, I don’t get “triggered” that easily. I see it as just another step on the way to the inevitable destruction of society. I see fashions as having played a major role.

Yes, I too agree that shorts in general are immodest.  Not that they would typically constitute any "occasion of sin" for girls who happen to behold their hairy legs, but, rather because I consider modesty to be a broader concept.  But these things are long enough where modesty is not a consideration really.

With regard to dignity, that's a little slippery.  If I am a farmer and wear grungy clothes or overalls, or if I just wear jeans in general, one might make the case that thy are "undignified".  But just as it would be perfectly appropriate to compromise dignity a bit so that a man can do farm work without wearing his Sunday best, so too I don't think there's any problem with wearing these knee-length shorts in order to run.  I do not consider this level of "indignity" to be sinful ... given the context.  Now, if these boys were to dress like this at, say, the grocery store, I would consider that slovenly and undignified, and perhaps a very slight sin with regard to being sloppy, but I'm not seeing any offense against modesty or against masculinity (these shorts do not appear at all feminine).  Dressing like that for Mass, of course, would certainly be unacceptable.  Now, those 1970s short shorts were both extremely immodest and effeminate ... to the point that the men wearing them could easily be taken for ɧoɱosɛҳųαƖs.  But I'm not seeing that with these either.

Generally I’m in agreement with you. Wearing a jogging suit would be a better choice. All are very good points you make!

There are a 1,000,000 "comforts" of modern life that one could argue erode catholicity.  Doesn't mean they are sinful.  They CAN be, but aren't necessarily.

I don’t agree with everything this lady says in her article, but I do agree with this part:

Shorts have a way of feminizing boys, softening them. In 1999 in my book, Immodesty, Satan’s Virtue, I wrote and still hold to today,
“Boys, to become men in the true sense, should be trained from a young age to be able to withstand the rigors of weather and discomfort. Even the discomforts of wearing pants; when it is very warm. We want our boys to grow up to become men who are strong, courageous and impervious to discomforts. “

https://www.littleflowersfamilypress.com/why-must-catholic-boys-men-be-modest/

But if boys grow up to be men without these qualities, as is the general rule nowadays, they are cupcakes, sissies, whiners, quitters, complainers, etc.

Wearing pants at all times is a meritorious training and a discipline for the development of masculinity and manly qualities (in addition to the expectation that traditional Catholics are rightly held to a higher standard - noblesse oblige).

I don't think this is being done for comfort in this case ... just to better enable them to compete in a particular endeavor.  I think that the assumption here is of wearing shorts on a regular basis because it's too "hot".  There seems to be too much conflation of concerns.  This title suggests that it's a "modesty" issue.  But then this thing about it turning them into sissies is a completely different concern.  As was the earlier comment that they have practical issues.

I can argue that using a power drill to drive in a few dozen screws makes me a "sissy" ... or that I feel that I have better use for the couple hours of my time this would save.  Or it softens women to do laundry using a washing machine.  Yeah, maybe, but what if a woman suddenly has time to homeschool instead of having to do laundry, dishes, etc. by hand every day?  

Yes, I too agree that shorts in general are immodest.  Not that they would typically constitute any "occasion of sin" for girls who happen to behold their hairy legs, but, rather because I consider modesty to be a broader concept.  But these things are long enough where modesty is not a consideration really.

With regard to dignity, that's a little slippery.  If I am a farmer and wear grungy clothes or overalls, or if I just wear jeans in general, one might make the case that thy are "undignified".  But just as it would be perfectly appropriate to compromise dignity a bit so that a man can do farm work without wearing his Sunday best, so too I don't think there's any problem with wearing these knee-length shorts in order to run.  I do not consider this level of "indignity" to be sinful ... given the context.  Now, if these boys were to dress like this at, say, the grocery store, I would consider that slovenly and undignified, and perhaps a very slight sin with regard to being sloppy, but I'm not seeing any offense against modesty or against masculinity (these shorts do not appear at all feminine).  Dressing like that for Mass, of course, would certainly be unacceptable.  Now, those 1970s short shorts were both extremely immodest and effeminate ... to the point that the men wearing them could easily be taken for ɧoɱosɛҳųαƖs.  But I'm not seeing that with these either.

Your only focus on everything seems to be a whether it is sinful or not. Like I said: 

By the way, by your only WHY, immodesty, you would not have a leg to stand on with regard to women wearing loose fitting pants. Bp. Williamson also taught that women can't wear pants, and it was not only because of immodesty like for instance tight form fitting jeans, it was because pants are the clothing on men. In this case of the shorts, there is a similar WHY they should not be worn by men,  it is because they are the clothes of children, my #2 above.

If that were true, they would be wearing jogging pants.

Not sure ... depends on the type of running they're doing I would imagine.  I could see the pant legs below the knee constantly flapping against ones lower legs to be a problem and a distraction on a vigorous run.  Of if you're on a cross-country type run, going up and down hills and perhaps running into things on the terrain, I could see longer pants catching on stuff or even getting stepped on by the runner.  I have little problem with the outfit.  What I'm more concerned about is the constant emphasis on the worldly aspects being so emphasized in the neo-SSPX.  It's like promoting the seminary by showing mostly pictures of seminarians playing hockey and soccer, etc. ... and de-emphasizing the studies and the spiritual formation.

I get the uncanonical altar and cringe-worthy motorcycle design, but I really don't understand what is wrong with short pants. How are you supposed to go around in the rain? Would you rather that we all wore skirts? Around the world, countless people are in heresy and faithlessness, on the way to hell... but there are people wasting their time and energy about this?! Lederhosen have been used since when...And where is the papal condemnation?! Please, I beg that someone show me where in the Bible, or in any ecuмenical or regional council, or in any papal bull or encyclical, or in the compilations of Denziger, Ott, Tanquery, etc... does it say that men can't wear short pants (long enough to reach the knee), and I will take immediate action!

I can argue that using a power drill to drive in a few dozen screws makes me a "sissy"

Exactly.  And computerized car engines, remote controls of all kinds, automatic garage doors, computers of all types, instant coffee and let's not forget the steam engine.
.

Lederhosen have been used since when...And where is the papal condemnation?!

Exactly.  And Scottish kilts too.  Or what about the 1700-1800s when guys wore shorts to their knees, with knee-high white socks?  (i.e. Benjamin Franklin times)