There have been many different varieties of socialism. You can go back to versions that even preceded the Utopian socialisms of the first half of the 19th century, which were followed for a long time by the dominance of Marxian socialism. Modern socialisms, are mostly some form of Marxian socialism, each revised or modified in some way. You are simply going to have to accept that the USSR formed one version of these socialisms. Mussolini, who was originally a socialist - indeed the editor of Avanti the chief newspaper of Italian socialism 100 years ago - openly admitted that fascism arose from socialism. Not surprisingly, the two have much in common. Socialism and fascism were two branches of the same modern totalitarian revolutionary dictatorial system. And the arguments between fascists and socialists often appeared as some sort of bizarre family feud. Their similarities are basic; their differences reflect mostly differences in emphasis, degree, and sometimes the enemies they claimed to struggle against. They both embraced mass murder of innocent civilians on an unprecedented industrial scale as fundamental aspects of their respective policies and revolutions. It is true that some socialists have attempted to distance themselves from this sorry part of the history of socialism - and who could blame them? - nevertheless, these efforts do not mean that the Soviet Union was not socialist. At best, modern socialists can say that they prefer a different version of socialism than that practiced in the USSR, or China, or Cambodia, or Albania, or Eastern Europe (which all differ slightly from each other).
There is no socialism in "the pure sense." You might as well be talking about some silly fantasy or delusion. There is also no pure fascism. There are, however, the practices of socialism in history and the practices of fascism in history. These we can compare. If you want to compare fantasy socialism to real fascism you'll end up going nowhere and looking quite foolish.
Why are you referring to my last point and invoking Nazis? My point, if you'll read it again, is clearly referring to the Soviet Union and not to National Socialist Germany.