Can you point me to that legislation please, so I can have a look at it.
That's a fair point. The real issue though is what happens when you didn't break their user agreement, but they _think_ you did, what happens then?
Banning a small percentage of users unfairly won't have an impact on their business, particularly if they are a huge company with a near Monopoly, and legislation is weak, or unclear. Unless the users work together to defend each other. That won't happen if the majority who haven't been unfairly treated just says "well, it works fine for me and they seem like nice people". Large corporations feed on this sort of apathy.
Unfortunately, companies run by great guys sometimes get bought buy the spawn of Satan, then everything goes to hell in a hand basket.
I can do all sorts of things to minimise the risk of fire in my house, I can also take out insurance. I can't DO anything to minimise risks associated with a digital distribution system like Steam... other than choose not to use it, which is what I do.