Why are (some) men so attached to their sperm?

I know that some donate sperm and that they don't mind having children out there but some are very much against it and say they wouldn't feel right knowing their kid is out there (even though they have no parental rights over him or her once the sperm is donated).

My friend wants to have a biological baby but her husband shoots blanks. He wants her to adopt and she doesn't want to and wants a baby via in vitro. He's completely against it because it's another man's sperm and another man's baby.

I really don't understand and neither does she. Can you please explain to us?

EDIT: Not to sound cheesy, but I've actually learned a lot from the men replying to this post. I feel like I have a whole new perspective on the way men think. Not to say I know what they're thinking, of course it's impossible to know what any person is thinking at any given time. But even if there were some bits that sounded unintelligible or even ignorant I don't wish to hide them because they played their part in seeking greater knowledge. I'm glad I've been able to learn something from all of this.