Does one have to be an iconoclast or revolutionary these days to be validly left? I consider myself to be left of center, and very much in favor of progressive policies.

Left and right are always relative terms. I like to describe those who feel like they are or could be represented by a political party in the governing coalition of an average western liberal democracy, as the "non plus ultra" left. This comes from the old story of the Pillars of Hercules on either side of the Strait of Gibraltar, which were said to bear the warning "non plus ultra" — "nothing further beyond". For as far as people knew back then, there truly was no land for sailors to find further to the west of that point; but now Europeans are well aware that there is a whole gargantuan continent across the Atlantic, a continent that makes the idea of the Iberian peninsula and the Maghreb as the furthest western extent of land in the world seem downright laughable.

And so those who call themselves left-wing, but who would be comfortably represented in the government of a liberal democracy... Well, they would be left-wing by the standards of the beliefs which can be comfortably represented in the government of such a country. So they're left-wing to that extent. But in the grand scheme of things, they're no further left of the parliamentary center compared to Marxists and anarchists, than Gibraltar is west of the Prime Meridian compared to Alaska. As I'd see it, frankly, all the beliefs which can find success in a liberal democracy, can be said to occupy the same "continent" of politics; and all those beliefs which cannot, can be said to occupy a different "continent", and those on the former continent would certainly stand to benefit from "crossing the sea", so to speak.