The Stalinists that cling to the past are of a dieing breed. Totally irrelevant. But, at least in the Netherlands, there are "streetwise" Stalinists that have a more healthy attitude towards the workers movement, although still handicapped politically. I think we should engage in debates with this latter variant.
Also, the second world war was won despite Stalin's policies than because of it. The purge in the late thirties killed many capable army leaders. There was a good reason why the the Soviet Union had by far most casualties in the war.