It's quite obvious that most of the posts on that topic are made by either clueless goobs or armchair ninjas who know nothing about ballistics OR criminal trends...
The civilian-legal rounds fired by a 5.7 pistol won't penetrate body armor. End of discussion.
When fired by a rifle, they sometimes will, depending on the armor and the location of the hit. And as a general rule, BGs don't use rifles. If rifles that will defeat Level II body armor should all be banned, then we need to ban Ruger 10/22s and ALL rifles more powerful than that (30-30, 30-06, .308, etc)...
Criminals generally don't get their handguns from dealers, and there are so few FN 5.7s in circulation that there is almost no second-hand market. So the chances of a criminal getting one is essentially non-existent.
And the rounds for these firearms are harder to find than high-quality .380 auto defense rounds, so even if a BG could get his hands on one of these pistols, he'd have a heck of a time using it without ammo....
ATS is good for a laugh. But as a source of factual info, or meaningful commentary, it's about as useful as snowshoes in Miami...