If the FBI prosecutes for it, it doesn't really count. That's kind of like saying you can't eat at a restaurant because some chefs poison their customers. Sure, but it's illegal and not the typical state of affairs.
I don't believe that kickbacks are common (I'll change my stance if evidence shows that they are wide-spread), even for on-label uses. I'm pretty sure they're still considered a serious ethics violation and probably illegal.
A slightly different twist: a friend of mine is a pharmacist and he was decrying the end of free lunches provided by pharma companies after he finished first year (a few years ago). The influence of drug companies may exert is a recognized problem, even where it doesn't take the cash for prescription model (that I agree with you is probably illegal but I haven't looked into it). I do think it's likely though that there are creative ways out there that drug companies have come up with to encourage prescriptions.
