A lot of very narrow-minded, sheltered comments on here, offset by some nice, positive attitudes as well. :)
A friend of mine has done this - she has a 1YO DS and is expecting a second child - both fathered by the same donor. She doesn't know what he looks like, but knows all sorts of other things about him - his medical history, his family, etc.
She is lovely. Warm-hearted, kind, loving. A great Mum, who has lots of support from her lovely parents, and an amazing male role model in her Dad. I've known her family since childhood and they're one in a million. She (my friend ) has two adopted siblings (and one blood sibling). Her parents have set her an amazing example. Unfortunately she has not (yet) met anyone she wants to share her life with, so she has gone down this route. We're not in the UK, but suffice to say this was all done privately and paid for by herself (she has a very good, professional job, degree-educated, top of her game plus does volunteer work).
The way I see it is this... The world needs MORE children raised in happy homes, by parents or a parent who loves and cherishes them and who parent/s them well. These sorts of children pretty much inevitably turn into happy, well-adjusted adults who make a positive contribution to society. The world is crying out for more people like this, not less.
Some people need to put their blinkers down and their prejudices to one side in order to see that there is more than one way to do things. None of us are perfect, but I see a lot less wrong with this scenario than with many others. And to be honest, anyone who would argue against what my friend has done is not worth knowing, IMO.