Iíll agree with you on the courtesy thing: follow the rules or go home. The flip side to that if the particular game that day uniform/costume & gear requirements are not specified aside from a color then snubbing the new guys wonít help the overall cause. Some guys are playing it as a sport and some as a game. Iíd lay the onus on the new guys to do as much research as they can before and between games, and the old guard to do a little mentoring.
Personally Iíve never experienced or observed any snubbing, so itís all an academic exercise to me. Most of the games have been skirmishes where Iíve been to Iíve been relegated to the terrorist/civilian/PMC side where mixed gear falls tolerated & recommended. And it works. I want to Ďearn my wayí in the milsim side of things, not just by buying my way into the game but by earning my dues in the blood & mud.
One advantage airsoft has over Facebook are the Dislike buttons. Theyíre called triggers.