I’ve been through this a few times: Usenet, Digg, Reddit. They started off small and stayed mostly civil even though there is a wide range of opinion. Then they start growing rapidly and people see an opportunity to “get their message out”, whether that’s spam, personal aggrandizement, a political message, or whatever: exploitation vs participation. After a while it becomes just too much for some people, so they find somewhere else to congregate.

But is this a bad thing? Even if Lemmy 'doesn't survive' (which I think is a fair way off, personally) something else will take its place. Something always does; ICQ dies, people move to AOL. Digg dies, people go to reddit, Myspace to Facebook and so on. Look at the absolute graveyards of websites where people used to congregate and play games and talk: Battle.net, Mplayer, WON.net, Digg, Usenet, AOL messenger, ICQ, Myspace, there are dozens of these things that, at the time, we felt like would always be there.

Enjoy it while it's here. Make it the best place you can.