You could say that depressives can’t help their condition because it ‘s an illness. Even so, it’s interesting that these guys all suffered recurring depression, including features of paranoia, and became drug addicts as a result. In addition Mussolini carried an incurable form of syphilis from the time of WW1 and took drugs throughout his life to ameliorate the worst symptoms. There you are: something else they had in common – they were all drug addicts.
About syphilis, Lenin the virtual dictator of USSR had died from it in 1924. There is recent evidence that Hitler suffered from it, which could explain his mental confusion and muscular tumors towards the end of his life: previously attributed to Parkinson’s disease. If you dig around, you may find that Hitler, Mussolini, and Stalin all caught syphilis. But I’m not saying that here.
A personal observation: it’s interesting that their political tendencies, although very different, made no difference to their tyrannical and murderous regimes. Is there a lesson here for any of us who has an inherent preference for Left or Right wing politics? Neither tendency produces good guys, necessarily.
In response to another answer, Mussolini was quoted in Corriera della Sera to say, “I have been a racist since 1921. How can they think I’m imitating Hitler. We must give Italians a sense of their race.”
After the end of the war, his private secretary recalled a comment made in 1940, “These disgusting Jews, I must destroy them all.” It seems to have been a personal prejudice; not an official policy.
As regards Stalin, there is evidence from Trotsky’s letters, and those of his friends, that Stalin used the fact that Trotsky was a Jew to turn some of his Young Communists against him. Stalin couldn’t use the ploy openly because Marx had been a Jew also, although Prussian, but he made adverse reference to Jewishness quite frequently right up to the end of his life. It was a personal prejudice; not an official policy. But in a dictatorship, such a personal prejudice was dangerous – especially if your name was Trotsky.