There's no going back

Does it make sense to consider one's self 'on the left' because one identifies politically with various founding fathers of the left, various leftists from another time? Mitchell Cohen, after criticizing some recent attitudes on the left, writes:

But let me be clear: I am “left.” I still have no problem when someone describes me with the “s” word—socialist—although I don’t much care if you call me a social democrat, left-liberal, or some other proximate term. My “leftism” comes from a commitment to—and an ethos of—democratic humanism and social egalitarianism.

What I care about is the reinvention of the best values of the historical left—legacies of British Labour, of the Swedish Social Democrats, of Jean Jaurès and Léon Blum in France, of Eduard Bernstein and Willy Brandt in Germany, of what has always been the relatively small (alas!) tribe in the U.S. associated like Eugene V. Debs, Norman Thomas, Michael Harrington, and Irving Howe.

This is all well and good until you consider that the left is by definition about a belief in progress, in revolution, in scrapping the old in favor of the new. By contemporary standards of any 'left,' the left that preceded it was racist, pro-capitalist, or otherwise acted in ways that would, in this later period, be considered right-wing. Imagine how, once upon a time, you could be on the left but not believe in women's right to vote! Or, you could be liberal and pro-colonialism! And even not that long ago, the pro-Israel segment of American society, aka Jews and Co., were inevitably associated with the left. Amazing!

It's entirely reasonable, by leftist standards, to seek reform of the left itself. But to seek a reform that is a return to original principles, i.e. a reform that is by its very nature reactionary, might well contradict a good part of what it means to be on the left.

Thoughts?