I don't think this was just happenstance. You don't just randomly become a misogynist because of mental illness. This kind of hatred is cultivated over time through what you are consciously and subconsciously taught and conclusions you are making about the world around you. That level of hatred eventually devolves into something clinically diagnosable sure but I don't think it's right to say that he just "happened" to direct his hatred at women.
I agree with you though on destigmatizing mental illness and that our systems are not set up to deal with cases like this well enough.