nowhere does it mention "oh btw if you don't own the rights don't do it", that's hidden on the terms of service page.
Are you surprised that when you buy a knife, it doesn't come with a warning explaining that you can't stab people with it?
Uploading music you don't have a redistribution license for is not against the ToS, it's against the law. You're supposed to know it in the first place.
If you go to a website and click "My Music" and then it says "Upload your music collection to be accessed from anywhere" and doesn't explicitly state "It's illegal to upload music you are not licensed to distribute, you're posting music to be listened to by any user of Grooveshark" and then distributes every upload you submit to every user of that website I would not compare that to buying a knife and not being told it can kill people.
Are you surprised that when you buy a knife, it doesn't come with a warning explaining that you can't stab people with it? Uploading music you don't have a redistribution license for is not against the ToS, it's against the law. You're supposed to know it in the first place.