Most Helpful Guy
Yes. Sometimes. But in such cases I'm not entirely sure I want to, so it's probably for the best.
Most Helpful Girl
Most people don't see the point in being in a relationship in which they aren't happy and that's understandable because that's how relationships work. They can't be one sided.
Even if you do feel really bad for the person in question and end up going out with them because you believe in chances (been there) and you're not completely certain that these people aren't capable of making you happy and content. If it works out for you then great but often, you'll find that it only gets more complicated if you're certain that the person is not for you. They get more attached and it's hard to break up the relationship without crushing their hearts.
So yeah sometimes it's better not to give things a shot when you know things just won't work. It may sound harsh but rejection is a part of life and you have to work your way through it and find someone new.