I think the moment someone thinks people who hold opinions other then their own are stupid or evil or bad in someway for holding those opinions, they are an asshole. It isn't necessarily an extremist thing either. There are plenty of people who aren't extreme who think all Republicans are stupid (sure, lets see you perform the Neuro-surgery that Ben Carson does.) and there are people with extreme political views who are perfectly nice and can engage with people in a fine rational manner, Noam Chomsky comes to mind. He's probably never raised his voice in his life.
I think the assholery really comes into play when it involves how you view the other side rather then what positions you yourself holds.
I think the assholery really comes into play when it involves how you view the other side rather then what positions you yourself holds.