I'm not sure why such a obvious statement of fact can still cause so much offence among some of those who describe themselves as democratic socialists, but it does. I suppose here we are mainly talking about not the intelligent left, but the historically illiterate 'Twitterati' - who seem, tragically, to include among their number those who now run the British Conservative Party.
Why does it matter? Because not telling the truth about the past always matters. We're back to the nightmare vision of George Orwell again:
“He who controls the past controls the future.
He who controls the present controls the past.”
Of course, to acknowledge Hitler and Mussolini's dependence on a warped form of socialist ideology with added elements of radical Teutonic or Roman paganism, does tend to deprive the same group of historical illiterates of the opportunity of branding all their opponents on the traditional, democratic right - in true 1960s style - as 'fascists.'
But, of course, we know that fascism and Nazism were not right wing, conservative ideologies at all and least of all, despite their initial, respectable camouflage, did they spring from the mainstream culture of western Christendom. The 1937 encyclical, Mit Brennender Sorge of Pope Pius XI (worth reading in full) made that very clear indeed:
"..Such is the rush of present-day life that it severs from the divine foundation of Revelation, not only morality, but also the theoretical and practical rights. We are especially referring to what is called the natural law, written by the Creator's hand on the tablet of the heart (Rom. ii. 14) and which reason, not blinded by sin or passion, can easily read. It is in the light of the commands of this natural law, that all positive law, whoever be the lawgiver, can be gauged in its moral content, and hence, in the authority it wields over conscience. Human laws in flagrant contradiction with the natural law are vitiated with a taint which no force, no power can mend. In the light of this principle one must judge the axiom, that "right is common utility," a proposition which may be given a correct significance, it means that what is morally indefensible, can never contribute to the good of the people. But ancient paganism acknowledged that the axiom, to be entirely true, must be reversed and be made to say: "Nothing can be useful, if it is not at the same time morally good" (Cicero, De Off. ii. 30). Emancipated from this oral rule, the principle would in international law carry a perpetual state of war between nations; for it ignores in national life, by confusion of right and utility, the basic fact that man as a person possesses rights he holds from God, and which any collectivity must protect against denial, suppression or neglect. To overlook this truth is to forget that the real common good ultimately takes its measure from man's nature, which balances personal rights and social obligations, and from the purpose of society, established for the benefit of human nature. Society, was intended by the Creator for the full development of individual possibilities, and for the social benefits, which by a give and take process, every one can claim for his own sake and that of others. Higher and more general values, which collectivity alone can provide, also derive from the Creator for the good of man, and for the full development, natural and supernatural, and the realization of his perfection. To neglect this order is to shake the pillars on which society rests, and to compromise social tranquillity, security and existence..."Read it all: in very different political circumstances it still speaks to us powerfully today...