Friends versus allies

It seems it is hard to find good friends. I'm not a very social person, so I don't interact with people very frequently outside of school or work. When I do get to know friends and neighbors, there are inevitably politics that arise among them -- someone doesn't like someone else for some random reason. And it is hard to find someone who doesn't eventually do something I don't like myself.

Could it be easier to simply find allies? If I have an interest in learning or accomplishing something, maybe I could forget about finding friends and just focus on finding people who share my interest. I could ignore someone's negative character traits but just seek interactions with him to advance my goals. It seems that any group with politics -- whether a neighborhood, an office, or a dinner club -- really just functions by getting along rather than trying to be Best Friends Forever.

But shouldn't I draw the line somewhere? Is there a point at which someone is so rude that associating with them could hurt me? When is one "judged by the company you keep"?