I haven't read the whole thread, but I have 2 children by sperm donor.
My first child was born when I was with my ex, who was sterile and agreed to sperm donation to have a child. During my pregnancy he bailed out and decided not to be a father after all, so we split up.
2.5 years later I hadn't met anyone new, and had just turned 40. I had never wanted DS1 to be an only child, especially as I was a single parent with a very small family myself. I had a brother (died when I was 19) and we were always very close, so I really liked the idea of having a sibling for DS.
So I went back to the clinic, and had a few more cycles of treatment, using a different donor as my original one didn't want to donate any more apparently. I had DS2 18 months later.
I did all of this through a clinic, and obviously it was private as NHS funding isn't available.
I briefly looked into the "agencies" who claim to introduce donors to women, but they all seemed dodgy.
I think it's only really safe if you use a proper clinic.
DS1 was born before the anonymity law changed, so he will never be able to find out who is father is. DS2 was born after the law change, so when he's 18 he can get the donor's details from the clinic if he wants to.
I'm sure plenty of people will say that what I did was selfish, putting my own desire for children above my children's potential desire to have a father. Maybe it was selfish, but I give my children a very good life. They are my world, everything I do is for them. I endeavour to be Mum and Dad, playing football, climbing trees, playing Star Wars - all the "boy stuff" as well as the Mummy stuff. Of course it wasn't how I'd planned my life to be, but there are some positives. My boys never hear arguments, they will never lie in bed at night listening to raised voices, they are parented consistently. You only have to look on the Relationships forum to see that having 2 parents isn't always a recipe for joy and happiness!
I also briefly looked into adoption, but most agencies don't like single parents, and would only offer "difficult to place" children. I didn't think that would be fair on the child, me or DS1.
I think it's very easy for people to judge my decision, if they've never been in the position of being single and watching the reproductive years fly by.