In addition to the good constitutional reasons already given for not regulating a batman suit, there's also a little bit of cross-discipline history.
A buddy of mine recalls hearing that he had no business wearing 5.11 "tactical" gear as he wasn't LE. He felt compelled to point out that the stuff wasn't "tactical" when he bought it - it was for mountaineering and rock climbing. Turned out it had another use. So suddenly, all the rock climbers have to get along without? How about Royal Robbins? Isn't climbing like, unh, what he
does?
Nobody asked Joe Willy if he was defending himself from anti-aircraft fire when he took to wearing a flak jacket. (NY Jets, pantyhose model, giving away my age here.)
Nascar drivers like Nomex just like firefighters do.
It doesn't take a big stretch to picture numerous non-ninja uses for batman fiber. Professional athletes - they're already using kevlar. Spelunkers. Get creative.
I've no issue with civvies getting the stuff and I view mall ninjas with benign amusement. It's never been about
need but when one accepts the government tinkering with the mall ninjas' playthings, one runs the risk of losing all the other uses that even <gasp> Tom Diaz might not have an issue with.
Body armor? Can't hurt anybody and for all you know, I'm diving doing shark research. Nobody's business but mine.
But the benign uses angle needs to be brought up - gives me great milage with the occasional million mom (this is Texas; the sightings are rare).