People who take a position on any issue outside of what might be called centrist and refuse to consider changing their minds have only two choices. If they believe they are right, they'll steadfastly defend their position. They'll stay on point. However, if they're confronted with an argument against which they have no defense, they are lost with only one option available to them.
The idea of entertaining a different, much less an anathematic ideology, scares them. It isn't safe. It shakes their world because they need to be right. So instead of considering that they may be wrong, even a bit, they strike out however they can. They'll abandon all reason and initiate an attack.
They do so because they fear opposing ideas might deserve consideration, rendering their ideas less worthy. In their minds, the worth of their ideology is totally predicated on the premise that other ideas are worthless.
Rigid ideologies own many of us today because they allow it. From religious fanaticism, to rabid politics, to irresponsible behaviors, they mindlessly fall in line like worker ants. They box themselves into a corner where attack is their only option. Attacking can be outright physical violence or the more subtle practice of mocking others for their beliefs. By mocking they assume a level of superiority over those they mock. It's intended to do that, and to appease an agreeable audience. The ideologies own the mocker who accepts that subservient role, believing being "right" is akin to being safe.
Richard Smith, Normal