Did you also remind your teachers in grade school and high school when they forgot to hand out homework on Friday afternoons?

I guess there's nothing wrong with what you did, but if I were in your shoes I certainly would have stopped short of pointing out the person. You never know what you'll encounter then... If that person had been a terrorist, it's likely that s/he wouldn't have been caught anyway as their weapons would have probably already been stashed elsewhere. And if they had gotten on your flight with bad intentions, guess who would have been one of the first to feel the wrath?

It's simply not worth the trouble and, quite honestly, personal risk to get involved to that extent-- especially since (I'm assuming) terminal security isn't your job...