Well, I do feel sorry when someone spins due to pressure I put on him, but only because the fight is then over. And at the same time I'm happy to gain the position. A clean overtaking maneuvre, however, is more rewarding than gaining due to the car in front messing up. (Not that I speak from experience, it usually only happens with back-markers for me.)
I don't feel sorry for the driver personnally. I think it's part of race craft to put pressure on someone, and it's not easy. In order to do it effectively you have to be close to the car which makes it harder to hit apices, braking points etc. If you can pull that off cleanly, power to you, I'd say.
Likewise, it takes race craft to not mess up when someone is pressuring hard. That is an area where I have to do a lot of learning still. And if I spin because someone put pressure on me (which happens too often), I only blame myself.