Michael O Church once lost a job due to a "back-channel reference check", so that explains why he's so hostile to them.To tell the whole story... "you should see the other guy." :)
I did eventually get my revenge. Six months later when I had the money, I hired a PI to figure out who gave the bad back-channel reference (it wasn't even someone I worked under) and found out that he was sleeping with one of his subordinates. Had the news dropped at his work, to his wife, and at his kids' school on the same afternoon. God works through people.
By giving a negative back-channel reference, you and your employer might be susceptible to a lawsuit. However, actually suing a former employer for something like that is probably a bad idea, because (1) it'd be hard to prove it (2) it would make you even less employable when other people find out about the lawsuit.
A termination lawsuit makes you less employable. I don't know that the same holds over a bad reference, because pretty much anyone would sue someone who damaged their careers in such a lasting and petty way. Getting fired is something that happens to everyone and while most of us aren't fired in an illegal way or for illegal reasons, most people will be fired in an unjust way at least once in a 40-year career, so the prevailing attitude (right or wrong) is that a successful, competent person will just dust himself off and find another job. Bad reference issues are much less common and most people (the rhetorical "reasonable man") would agree that you have to do something permanent and brutal about that.
Wrongful T lawsuits are dangerous to your career because (a) every company or manager will have to fire someone, given enough time, so it's far from clear that your opponent did anything wrong (b) they bring a lot of dirty laundry (on you and the company) into the public, and if there's no dirt on you, they make something up, and (c) your odds of winning aren't good unless you can easily prove discrimination.
When you sue over a bad reference, you're suing an individual (not "an employer") and you're also suing over something that would lead pretty much anyone to lawyer up, so the air about you isn't "he got let go and sued his company" but "someone tried to fuck up his reputation and he fought back".