I agree with you that mental illness does not equate to crime and most people who commit violent crime are not necessarily suffering from a psychological condition. People can kill for reasons as simple and seemingly petty as money or jealousy - and if everyone who committed crime was found to mentally ill our psychiatric facilities would be overflowing.
But it would be stupid and wrong to deny that mental illness contributed to Lubitz’s actions; he obviously was not well, had been taking anti-depressants and there’s proof that he was being treated/had previously been treated for psychological problems, and according to the hospital where he received the treatment, it wasn’t simply for depression. So obviously there was something more severe happening to him. And it wasn’t just his mental illness that contributed to this; it was likely multiple factors like work/personal stress and his breakup with his girlfriend may have been a trigger - with mass murders there’s usually a trigger or event that sets them off even if they’ve been fantasizing or planning to kill for a long time. That doesn’t mean it was his girlfriends fault, no way in hell - but these events can all set disturbed people like Lubitz off.
And when we acknowledge that mental illness was a factor in Lubitz’s crime, WE ARE NOT EXCUSING HIS ACTIONS. So if anyone sends me a message suggesting that I’m minimizing or excusing his crimes by saying he was mentally ill, then fucking don’t. It’s an explanation and one we need in order to help stop shit like this from happening in the future.
People commit crime for multitudes of reasons, and mental illness is one of them but a tiny minority (usually a byproduct of crime/criminal lifestyle but not the main cause), and people who are mentally ill should not be stigmatized or assumed to be violent or dangerous because of their conditions. But it’s just as important to acknowledge that Lubitz was mentally ill so we can learn from this; the motivations, the signs, the treatments he received, how effective they were, what could have been done better to prevent this etc. There is nothing wrong with people spreading this discussion because it is a FACT of this case: he was mentally ill. You cant dismiss or minimize facts and ignore them in favour of explanations that are more comfortable for you or your situation because we need to fully understand these crimes and their contributing factors in order to better prevent them from happening again.