What strikes me as wrong* about this kind of law is that they add an additional crime (and the accompanying punishment) to a single act or harm. Wander around town in body armor, that’s just fine. However, if you decide to rob a bank while you’re out, wearing the body armor becomes an additional penalty.
*by wrong, I mean contrary to the legal theory and principles, as I understand them. Yes, it seems kind of stupid and weird that a single act of burglary result in charges of: breaking and entering, trespassing, as well as theft. But I can understand the logic (as was explained to me before in another thread) that those are separate harms and need to be addressed individually. Just wearing body armor, or carrying a gun doesn’t create additional harm, or constitute a different sort of violation (if these laws didn’t exist).
I think the problem is just in the specific way they’ve chosen to phrase it.
If we say that wearing body armour is not illegal, but if worn in the course of a crime it could be considered proof of intent, I think the OP’s objection no longer applies.
Like if someone is arrested in the course of trying to kidnap someone, and they find a dungeon in his house prepped for keeping someone for a long time…well that’s going affect sentencing since it implies planning, an intention to commit more serious crimes etc. Regardless of whether owning a dungeon is illegal. (sorry for the dark example)
The body armour also shows planning; it wasn’t an opportunistic crime, as well as an intention to resist arrest.