Well the "problem" at least for me is the fact those feelings are really hard to turn off. I know at least for me crushs tend to develop on people. I don't know that well. I mean that's really what a crush is, a visceral response to someone's first impression or looks, am I wrong? So even when further knowledge makes it pretty clear that said individual would be a poor choice for romantic partner it does nt turn the feelings off. And then when said individual starts to make advances on someone else... Ouch. That never feels good.
But you and I have to remember. First it is more than likely that the person didn't know. Or have any idea. So they really can't be faulted for any sort of secondary hurt feee fees. And the second thing to remember is that you are a bad ass and awesome and anyone is fool to pass on the strength, compasion and friendship you have to offer. So their loss :-p