The idea that employers will fire you for justifiable reasons when the reality is that they are firing for unjustifiable reasons is far more than simple conspiracy theory. There are numerous cases of people winning discrimination lawsuits because such firings didn't cover up good enough and lawyers were able to prove the actual reasoning. I do not find it unreasonable to think that many more cases weren't caught because the individual either didn't have funds to fight back or tracks were covered well enough the jury wasn't convinced.