It's hard not to see this as a combination of selfishness and self-obsession, carried to extremes due to mental health issues and access to guns.
We hear about this sort of behaviour on MN daily - men convinced that women owe them something, that women aren't separate human beings but service robots at men's disposal.
Here the two additional factors were the mental health issues and access to guns.
But the vile misogyny was probably there to start with. Had those two additional issues not been present, this man would probably still have been selfish, self-pitying and abusive to his wife. I find it hard to believe he went from being a loving, appreciative, supportive husband and father to shooting her for not taking him seriously purely due to mental health issues. The underlying contempt for her as a human being was probably there at the start.
Imagine the carnage if 50 year old women started shooting people who weren't paying attention to them.
Indeed. But this would require women to be conditioned to believe (i) that other people owe them attention and (ii) that violence, as opposed to walking away, is an acceptable response if they aren't paid the attention they believe they are owed. So very unlikely.