As much as i like helping people out and especially friends, I just could not do it. That's going to be YOUR child running around out there! Could you handle not knowing what your child is being taught at home, how he/she is doing in school, their first date, wedding, etc.???
Here's another way to look at it...
If two gay men came to you and your wife and asked...Can we put one of our sperm into your wife and have a baby with her but we get to keep it...how would you feel about that? I see trouble in the future.
+100000 on the sperm bank. There's plenty of sperm out there, they don't need yours!