Post #4 nailed it right on the head. Look at cliques in high school. You have the jocks, the goths, the nerds, the stoners, the preps and many more groups. Somewhere everyone can fit in some sort of category. Yes, generally the jocks will pick on the nerds, but they have a support system within their own community where they understand each other and what each other is going through.
This also extends into the adult life where different people have different interests. It is rare that a professional sports player with hang out with a teacher or someone outside of their professional field, but that doesn't mean that when they volunteer their time at the local soup kitchen because they like to give back to their community, they won't start a relationship with a teacher who is there doing the same thing. The kicker is, they have been brought together by a common bond of something they feel is important and they can connect through that community.
Even people who don't feel as though they belong to any particular community aren't alone. There are other outcasts out there, they can find each other and start their own little cliques. Especially with how easy it is to connect with people via technology and the internet, it is hard to be a loner unless they actively try.
When they can't avoid alienation, it is my personal belief that at that point maybe they need to look within themselves to see if there is something about them that turns them off to other people. Is it something as simple as a make over or personal hygiene? Could it be deeper like a personality quark that may need to be worked on to improve themselves internally? It takes work to change, but if someone is unhappy being alienated, they need to self-examine and assess if it is something that can be changed so they are more approachable to other people.