The only way I could do it is with one of my gay friends if he really wanted to be a parent, at least I know them in RL, and know a smidgeon of the person (and family) they are. (Also for later, when the child needs info).
A sperm bank would be too anonymous for me, what about genetic diseases and stuff...
I'd hate to have a child going down the street wondering if any passersby could be family...
Remember watching a programme and a woman who'd been born that way always wondering if she might be related to a boyfriend... (worried about eventual children).
Also read an interesting article about offspring getting together in USA from donors who'd done it regularly (i.e. lots of children).
I did have a boss who had a child by donor insemination, then her partner did too, as far as I know they are one big happy family.
Another ex boss, gay and in a relationship has a daughter, he does co-parenting.
At the end of the day, how you deal with it is the key, make sure they don't grow up feeling different. If the love and care is there, that's what it's all about.
You have to be ready to deal with people's prejudices though....