Mass murderers appear to have affinities to either the far left or far right. I'm not seeing any politcal moderates among them. Most likely it is the hyperbolic language of political extremists that draws the crazies rather than the crazies being created by the ideology.
Marginalized, disaffected people with mental imbalances do tend to gravitate towards extremist groups. It's just a fact. Transnational terrorist groups count on it and actively recruit them. The same can be said for domestic hate groups. Yet as we can amply see, it's the loner type who can't even successfully assimilate into these domestic extremist groups who go lone wolf and commit these attacks. Even Timothy McVeigh was so extreme he was kicked out of the Michigan Militia and THEY called the FBI to say he was crazy!