I'm saying that new blood and new thoughts and new ideas should always be encouraged in any community, space, or location. Particularly when resources like physical space are very much finite. I think that any desire to freeze a community, space, or location in amber is unhealthy. Those with an interest in the future of a community, space, or location will not be identical to those who happen to be there at the moment or those who were there yesterday.
For an example, look at what that desire has done to the housing market of San Francisco.
Like, imagine if suddenly the fishing community decided to come en masse to HN and start talking and upvoting only fishing-related stories, while downvoting / flagging everything else. I think the present HN community should have the (moral) right to tell them to go and find their own spot, instead of taking over someone else's.