Yeah, IMO, go ahead and tell them in the thread, BUT most people don't seem to like that and even through PMs, you'll most likely get a not so nice reply.  I know what you're trying to do, and I comend you for your effort, but unfortunately, I will be surprised if you make a difference.  It's going to take the movement of the majority of that individual forum to get things to change, and that probably won't happen.
Don't mean to get your spirits down, but if I were you, I wouldn't expect people to look up at you just because you're telling people that they're breaking a rule.
(Oh, BTW, my guess would be that many of the people in this forum will say that it wouldn't be crapping, but once you leave here, you may not see such an overwhelming vote.)