Quoting Chuck Bass:" I think it would be different if he had actually had sex with her. No guy that knocks somebody up should ... [snip!] ... sperm donor if they had sex. I'm not saying it wasn't stupid (and illegal), but its not really in comparison to a deadbeat dad."
You open a can of worms though by allowing him off the hook. I know it is different but that doesn't mean guys won't claim that there was no sex involved.
I also think it was a poor decision on his part to not ensure that this couple was financially secure before handing over his sperm.