IMHO, there is absolutely nothing wrong with Facebook. You can argue that people can end up doing stupid things and getting involved with people they shouldn’t be getting involved with, but you can say that about everything.
If someone wants to do the wrong thing, they will do it, regardless of whether they have Facebook or texting or not. A responsible, smart person would not do stupid things. A responsible, smart person would not accept a friend request from a stranger or some guy. and if they are stupid enough to do that, they deserve whatever happens to them and the reputation they will get. (Sorry,it really bothers me when people do stupid things so I tend to get worked up about it)
Just be smart and do the right thing and you will be fine. And if you can’t trust yourself then you have bigger problems than Facebook.
As to the whole Facebook- shidduch thing. I don’t think it should be a big deal.