The nature of being a leftist today means you are collaborating with organized crime. The globalist criminal syndicate is a mafia like organization that controls national governments just like mafias controlled municipal governments back in the late 19th and early 20th century. They are the driving force behind all the leftist moves towards a totalitarian, one world government. Being a leftist in a Western culture means you must support crime, because all the politicians who represent socialist values are owned by the criminal syndicate. There are no independent, socialist leftists politicians. They are all completely controlled by the deep state/globalist cabal.
It's not a problem exclusive to the political left. Many on the political right are also controlled. But it is possible to be on the right, espouse extreme, limited government, and therefore have morals and ethics that prevent being captured by organized crime. These people are tolerated by the globalists as they are extremely few in number. Most officials can be bought or blackmailed into submission.
So no. You can't be a leftist without supporting terrorists and criminals, because the nature of the entirety of the political left movement (and much of the right) is criminal.