but I know a lot of guys who regularly donate to sperm banks
Have you ever asked them why they donate? Is it for the money? To believe their seeds will live on? To help women? Or just for fun?
Personally, i wouldn't have a problem if asked... but would i got to a clinic to do it on my own accord? Probably not, unless the money was good.
Anybody remember the story a couple of years ago on Dateline, and it was discovered the doctor that was doing the insemination had used his own sperm in like 30+ couples? Or the case in Europe (maybe Sweden), where the wrong sperm was given to a couple, and this white couple had a black kid? Anyways, lots of screwed up stories out there, and you'd expect something like that would be carefully regulated.