Go me, get credit for not paying attention
Seriously though I don't see the problem with replying to old posts unless they were for a game a year ago, and even then if someone wants to do the same thing it makes certain amount of sense.
To distance oneself from those without common sense you'd have to keep a good eye out for them, be very strict and not be afraid to boot them out. It probably wouldn't hurt if the good side got some publicity...
Maybe we could have a decent sized op of some sort with a bit of press as to the good sides, and in it stress the maturity and sense required. Worst case if some idiot gets himself in trouble with an airsoft gun people would have heard about the skillful and mature milsim of capable and competent adults first. I'm not a PR guy so I may be off, but makes sense to me.