I believe most Christian parents would not want their children using myspace because of the pedophiles and other sex offenders who can easily get on themselves. Trouble is, lots of parents, christian or otherwise, don't have a clue as to what their kids do in the privacy of their rooms.
Your last line is the sad part. True, but sad. I know a lady who's boys have her as a friend on their Myspace account. She also has a lot of their friends on her account.
If parents monitored more they could talk to and ask their child how they know who is on their list.
Except for bands on my own account I can say that I have met about 85% of the people that I have on my own friends list. It's like anything else on the Internet. The wrong people can use them for evil purposes. No matter how well intentioned. Ten years ago the Internet as a whole was considered evil and to be avoided by many people. This time it's specifically MySpace.
When my oldest is 14 I will probably tell him to wait a few more years to use myspace. Mostly because of the ads. But, that is my own decision. Not because someone else said so.