Carrying a self defense weapon isn't about being insecure, it's about being prepared. I'd rather have it and not need it than need it and not have it. Kind of the same concept as putting on your seat belt when you get in your car, or having fire extinguishers in your home. Would you consider that being insecure?
No.
Car + seatbelt = preparation
fire + extinguisher = preparation
people + plastic knuckles = Travis Bickle
Seriously, as has been pointed out:
a) plastic knuckles are not heavy enough to equal brass knuckles
b) you'll never get them on in time.
c) you'll get thrown in jail regardless of whether your theory about your legal loophole proves correct, at least for the night, just on possession.
d) if you use them in a fight you've practically guaranteed yourself a court trial where you'll be having to defend yourself against jailtime.
e) what kind of situation leads you to believe you're in realistic danger of getting into that heated of a physical altercation? Most of the time they just want your stuff. Why set up a situation where you're handing over a billfold with no harm to your person to one where you've raised the stakes to a life threatening street fight? Even with your magic plastic knuckles, they're still probably going to get some damage in on you if you raise the stakes. If you're at the bar let the bouncer do his job, he's getting paid for it, and has more experience.
f) If for some reason people are randomly attacking you, why not learn some basic sparring and self-defense skills that are with you instantly and permanently instead of having to try and find a weapon that unless you're a trained striker or a boxer, you probably won't even be able to take full advantage of anyway.
You've got way more to lose than to gain by escalating a situation, and contrary to what action movies may've taught you, you probably won't be walking away without a scratch even if you do win, which you probably won't against a person who regularly engages in beating people up.
Just out of curiosity, how many fights have you been in that've been unavoidable? And of those, how many would've had better outcomes (in every sense) if you'd had an "equalizer?" Okay, now how many of those since you've reached age 18?