Well spoken.

interacting with them does nothing but benefit them and the spread of their lies and propaganda. It brings nothing of value for anyone else.

I mostly agree, except:

These people are not leftist.

They are leftists, on top of the genocide they support they're also all for workers owning the means of production. Leftism isn't "when good," right isn't "when bad," left and right are economic distinctions symbolizing the people on one side and the aristocracy on the other. There can in fact be "bad leftists" just as there can be "bad rightoids." Bad people exist everywhere, not just at republican conventions.

These people are not leftist.

Why not?

Can't deradicalize extremists without engaging them. Not to say where and when that should happen, or that the moral argument is even relevant. As Popper said in the wake of WWII,

If we extend unlimited tolerance even to those who are intolerant, if we are not prepared to defend a tolerant society against the onslaught of the intolerant, then the tolerant will be destroyed, and tolerance with them.—In this formulation, I do not imply, for instance, that we should always suppress the utterance of intolerant philosophies; as long as we can counter them by rational argument and keep them in check by public opinion, suppression would certainly be most unwise. But we should claim the right to suppress them if necessary even by force; for it may easily turn out that they are not prepared to meet us on the level of rational argument, but begin by denouncing all argument; they may forbid their followers to listen to rational argument, because it is deceptive, and teach them to answer arguments by the use of their fists or pistols. We should therefore claim, in the name of tolerance, the right not to tolerate the intolerant.