Can you explain in more detail? How could you owe steam money if you didn't finish the transaction? Did paypal somehow promise steam the money long enough to complete the transaction and then pull takesie-backsies?
The wrongs of Paypal have been mentioned, but most account blocking happens when a user violates Steam's TOS. Being an abusive jerk online while logged in and playing games. Or cheating.
Now, I think that's bullshit. You still paid for those games. I think you should own them. Completely. At most they should block you from their servers and their online play.
But with Steam you can easily download any title you own as many times as you like. Steam has its own problems, but this they got right. You can even back them up quite easily. (Man, that used to be a broken tool, but even it's good now.)
A TOS ban means your account is no longer usable.