It's certainly possible and even likely that there were people marching who just didn't give a fuck or were purposefully marching like shit, but as somebody who's served and marched plenty, you'd be surprised how quickly things get messy. It's easy, sure, but it can get out of hand quickly.
If one person goes out of step, especially with no cadence cues, those behind follow the one who's fucking up either consciously or subconsciously. Then the one who's leading the out of step march shuffles to get back in sync, forcing everybody behind them to have scramble to shuffle back into step. It's a domino effect.
Like I said, I won't say it's not possible that you're right, but if you were to watch any marching group you'd see people out of step in almost every case. Regardless of if they wanted to sabotage Trump's parade in this case, most of the people I served with wouldn't want to intentionally make their unit look like a bag of hammers - which sloppy marching does.
I think a lot of people are over analyzing this but like I said, it's still possible that what you believe is true.
Hey I don't have cats so it might be a bit different, but I've had a few dogs over the years and I figure it would be similar. Your cats probably associate the carriers with going to the vet which it sounds like they're not a fan of. Their thought process is probably carrier = vet = no thank you.
Have you tried to put them into the carrier without actually taking them to the vet? Drop some treats in there, let them explore it at their own pace, close it for a minute or two, and then either reward or praise them after release? Keep progressing to the point that treats are no longer required to lure them and they enter on their own, but still reward them on release. Rinse and repeat (and repeat and repeat and repeat). Over time they may change their attitude towards the carrier their mindset may turn into carrier = treats and praise.
If they're not food motivated you may have to use alternate bait such as toys or nip.