Other than you are correct that Antifa means anti fascist and they are basically anarchists.  But terrorist hate group?  Not hardly.  In fact its hard to call Antifa any kind of group any all.  There is no centralizes executive authority defining what Antifa is or what they do.  Antifa rose in Europe following WWII for one purpose only - to combat fascism and its white supremacist anti-immigrant supporters, by direct action and physical confrontation if necessary.  But by far its principle tactic is to expose and marginalize fascists and white supremists.  They want those people to lose their jobs and any standing in their community.    

They never had nor do they care about the left.  Antifa does not care about either the Republicans or the Democrats or any political party for that matter - although obviously quite a few in the day were communists for obvious reasons.  (Well obvious to those people who have a brain and actually exercise it.)

Antifa' purpose is very simple - combat fascism at its first inkling in a community.  It recognizes that Fascism and the White Supremecist movement that has been revitalized by the Trump presidency must be attacked and stopped at its very beginning before it can take hold.  They realize as should every American, that Hitler and Mussolini were voted into office and were enabled by a democratic parliamentary system.

Antifa only rises up as a reaction to the rise of fascism and white nationalism.  Once Trump and his implicit support of white nationalism is kicked to the curb, as well he should be, Antifa will fade away as it always does until the next fascist movement comes along.  Think of how many lives would have been saved it it was present in 1930s Germany.  How is that a bad thing?

Would Heather Heyer be alive today if Antifa didn't show up at a fascist rally?  That's not even a relevant or particularly intelligent question.  Antifa simply isn't part of that equation.