As a private company they can kick one off the service anyway, ToS (which they can easily modify on the fly) or not. I (probably mis-)read your post to mean the

As a private company they can kick one off the service anyway, ToS (which they can easily modify on the fly) or not. I (probably mis-)read your post to mean there was a clear legal problem with trying to modify the view to suit user tastes ("user content stays, ads go"). Folks doing this are fighting an uphill battle against stronger opponents who have powerful weapons (e.g., disable access), but it is not a hopeless battle -- there are examples of successful and profitable products built for filtering out force-fed content.