It really is true, because you can say anything you want (or nothing) about the reasons why you did it, and get away with it. You have to be a total moron not to get away with it.
This is terrible and unjustifiable, but that is how it is.
This is entirely a matter of what the law says, and in a discussion about adapting laws, it is a very weak argument.
If the law says you cannot lie about your reasons and that you must have them, then there is a means to enforce it. I mean, I could say I didn't rob a bank and get away with it due to lax laws and inadequate technology, but that doesn't mean it is impossible to protect banks from robbery. It means you reform the processes.
For instance, if employers went through independently regulated agencies to conduct hiring/firing/pay, then they wouldn't be able to make decisions like that and get away with it.
I'd love the processes to be reformed. But the fact remains that the law has no way to know your reasons for firing or not hiring someone as long as you tell them something vaguely plausible. You'd have to be an idiot.