legal website content/services?

Ok, recently on my website 420boards.com I've removed a forum called 'want
ads'. Basically it was a place for people to list what they want. In other
words someone would say, "I need a hookup, my email is
[email protected]" or something. No one could reply to the
messages, etc. The reason I removed this is because I began realizing that
since the owner of the site and it's host are U.S. based, the laws of the U.S.
will follow and some shit can happen since no matter how you look at it, I'd
be providing a way for buyers and sellers to meet.

I was going to disguise the service as like a wish list, so that people can say
something like, I wish I had a better hookup, and people could instant
message them or whatever. But I figured no matter what I'd be somehow
breaking the law this way.

After taking down the forum there was some discussion as to whether or not
it's something I should've done or not. Obviously since my name is on the
whois registration, I am responsible for ensuring the content on the site
meets certain criteria. (In other words I can't hookup whores with buyers,
can't allow gambling, can't hookup hitmen with contracts, etc.)

I took the easy way out by simply removing the forum instead of
investigating further. Does anyone have any more general knowledge to
shed on the subject? Thanks