You can always just do an end around these tedious discussions. What no one, even one who takes a "no true scotsman" approach to Stalin, can deny is that Stalin saw himself as a communist and a member of "the left."

ideology, and hoarded all the benefits of the people's labor for himself and those in power with him

Why not force everyone to preface this claims with a look at what Stalin viewed himself as doing?

At some point debates over ideology just boil down to language games so you can productively focus on that debate instead of failing to force someone to admit the evil person derives from his own side. This is especially true because this sort of gap between OP and Stalin is endemic to any sort of ideology and history (though it often takes a much weaker form).