Would saying bad things about my old gaming community affect their reputation?

been there done that,  if it's anything like the clans i was with, all the conversations are in messages on the forum chat board, and you can bet your life they'll have reasons for kicking you out, others in the community may refute your critism, it may be better just to leave, from my knowledge, nobody likes a moaner...

You will look like a bitter drama queen, stirring up trouble, and people will assume you deserved to get kicked out if you start going around talking about them like that. If your friends are so easily lost, they weren't really friends to begin with. Spend your energy looking for other people to play with and leave this group behind.