That... that's an incredibly lazy line of reasoning.

The OP is not Word of God on other peoples' politics. Moreover, if the OP said that, it wasn't here, so I can't see context. The intensifier 'full-blooded' is very suspect in particular.

You see we almost all agree on a lot of things... and so, these things cease to be considered political. In the space of what people want, to a great extent we're co-linear, with subtle deviations. Political movements define themselves by the difference from other political movements, and pull in a particular direction. So, two people can appear to be the same politically because they are pulling the same way. Alice, however, would stop after reaching her goal, which is close enough that she is still in substantial agreement with the common values, while Bob, who is more 'full-blooded' would continue pulling the same way until EVERYTHING was the difference he had from the common values, quite possibly orthogonal or facing the opposite way. Murder less important than keeping the soft boiled egg pointy side down, so to say.

Being 'full-blooded' in politics means you're a misguided horrible freak, no matter the party.

That being seen, it doesn't even stop there. The Stalinist Soviet Union was not even an over-extrapolation of Progressive values. What happened to the progressives in the Soviet Union?

They were murdered. Purged. They weren't even necessarily specifically targeted - almost everyone political was killed, jailed permanently, or (understandably) intimidated during the rise of Stalin. So by the time you get to Stalin, there are no movements allowed other than 'Whatever the State Says, Goes' and Stalin decides what the state says. This is undesirable for any political movement, and Stalinist-Russia is a cautionary tale to them all.

But if you don't buy that and think there were still political movements afloat, then... let's look at what Stalin did and compare it to Progressive values.

Stalin's most objectionable policies - murdering/imprisoning the opposition, and even people who had no political opinions for the crime of being inadequately productive, forcing people to work in specific ways, banning private ownership, preventing people from leaving or even having free movement...

These are diametrically opposite progressive values, by their own definitions.

The only one that comes even vaguely close is a regrettable tendency for some Progressives to place a low premium on privacy from the state. And that has become less popular lately (check progressive reactions to the NSA some time, you might be surprised).

ETA:

1) there are some who believe that Stalin was lied-about and misrepresented in the west. For them, they may support their imaginary version of Stalin, but they don't actually support what everyone else means when they think of Stalin)

2) Movements change over time. 80 years ago, a noticeable portion of progressives were eugenicists. Merely 35 years ago, Republicans' expectations of the proper tax rate were what modern Republicans now call Socialist.

3) Orwell wasn't simply recounting Stalinist Soviet Union - he was extrapolating out even from there. So even if your facts and opinions were all correct, it was an exaggeration. When playing on hard mode such as we are, avoid exaggeration.