Why would anyone prep if they didn't care the ship is on a collision course? It seems like they care a lot! That's why they prep!
The issue you're seeing seems to apply to everyone who isn't prepping, so it doesn't really seem like this is a problem that's caused by prepping. Normal people think everything is going to be fine and don't worry that the ship is on a collision course.
Also, you're thinking of community as some kind of exclusive thing, like a walled private community or something. It can't be that way if the goal is to survive. Normal people don't get to pick who is part of their community, it just sort of happens based on where we live and work and such. Building community means bringing in the people who don't have the means, not excluding them because they can't afford the entrance fee to the bunker or life raft. We don't have the luxury of being so selective.