On the day my friends, a lesbian couple, asked if I would donate sperm, I was delighted. As the donor, I didn't know if I had permission to grieve: they had and meeting someone when you're starting a family with someone.
While the use of sperm donation allows same sex female couples to build their families, there are many legal pitfalls that can arise in the process. Same sex.
There are a number of reasons why parents choose to conceive with a known sperm donor. Some want to have control over their choice of donor, but don't.