Stalin was INDEED an evolutionist! It was Darwin’s book that changed his life. Stalin was a Seminary student when he read Darwin’s book. In a letter he declared, “You must read it!”
Stalin may have started out that way, but when in power, obviously his ideology won instead of scientific facts. Stalin supported Lysenkoism, praised Lysenko, and placed him over the other biologists. Lysenko persecuted those who disagreed with his theory; some were arrested and sent to gulags. Lysenko was not relieved of his position until after Stalin's death.
Which tells us that during the time Stalin was a tyrant and a butcher, he wasn't an evolutionist, but a Lysenkoist. Using your logic, that discredits Lysenkoism and endorses evolution. But science doesn't need to do that - the scientific evidence quite clearly debunks Lysenkoism and supports evolution.
Don't be silly. Lysenko was an anti-Mendelian Marxist, just like the eugenist (and Darwin Medalist) Karl Pearson. I bet you aren't aware that J.B.S Haldane (another Darwin Medalist) published a defense of Lysenko in the early 40's.