I don't know, Kent. If we're playing analogies, then the difference between MySpace's 'dark alley' and New York as 'dark alley' seems artificial if not non-existent. New York City's government and the business who pay tax to it make millions if not billions of dollars enticing kids to buy whatever it is kids buy in New York City. It's owned by a large organisation that doesn't seem in any major way different from a large media company like News International. You are right about the third item you list, but it doesn't seem like a big concern. 
The problems that a site like MySpace has aren't going to be solved by technological means - if MySpace locked down their platform like MSN UK did with their chatrooms a few years ago - then everybody loses. MySpace loses because their users - or at least ones with more than a few brain cells - go elsewhere. Then the parents lose, because it becomes harder to track ten social networks than one. The kids gnash their teeth and think that the world has conspired against them having fun.
MySpace has about the same incident rate as any large city. We don't demand that New York City or Boston or London locks down their city and ensures that nothing bad happens within the confines of the city. We hope they take sensible and economical steps towards preventing as much crime as possible. The difference is that if you live in London, yo don't have a choice as to who runs the place - whichever buffoon the rest of the population choose becomes the ruler. But if the users stop liking MySpace, they can go elsewhere. Parents can tell their kids not to use the site if they have cause for concern.
MySpace has more limitations than the web at large. Huge chunks of the site can't be accessed without membership. When people are concerned about MySpace, they are actually concerned about the Internet. The difference is that the Internet doesn't have a puppet-master behind it that you can blame when stuff goes wrong.
