By default the servers are at normal difficult coop campaign mode. You can join in the server first and then vote to change difficulty or mode. We'll change some to pvp servers tomorrow on default.

binding a server to a community might be ok, but i think it would be more open if they used a search key instead. that way even if you don't want to join the steam community (for whatever reason), you may still host a lobby and use a search key to reserve the server.