Seriously? Do you really read the entire terms of service every time you sign up for a new service? Besides that, just because you have the legal right to do something to your customers doesn't mean it's a good idea. I mean, did you realize that most stores aren't obligated to take back returns? And yet, the biggest company in the world (Wal Mart) is very well-known for taking back anything. There have even been cases of people bringing back diapers claiming they were all used beforehand.
When it comes to TOS dealing with writing and publishing, yes, I do indeed read the entire TOS. When you go get a job, do you inquire into the terms and conditions?
I don't doubt there's piracy or unofficial uploading. But Scribd has also made a push to get self-published writers. And they miss the point someone downvoted.