The United states and Russia were enemies since at least 1948 or 1949, which was mainly because of differences in ideology, fight in Asia and the middle east and so on. Even after the Soviet union, along with the Warsaw pact, collapsed in 1991, Russia, since at least since Vladimir Putin became president, it has supported countries which USA has invaded since the 2000s, including Iraq, Syria, Libya and even Iran. While these are pretty obvious reasons for the establishment disliking Russia, there are hardly any reasons for an everyday liberal or democrat to do the same.
However, here's what you have to know. While Russia and the Russian people still might have a dream of a new Soviet like empire, Russia isn't the soviet union, in fact, ideologically it has shifted far away from communism, just like other members of the Warsaw pact like Poland and Hungary. While there are many reasons that Russians and Non-Russians alike dislike Putin, mainly because of corruption and him growing pretty authoritarian over the years, I doubt that's the reason that the radical left dislikes Russia.
The reasons the radical SJWs dislike Russia is because, just as I've mentioned, it's not the Soviet union, it's not communist, and it doesn't align with their ideals. It doesn't support open borders, socialism, minority identity politics and probably the biggest one of all, it is still Christian, even after almost a century of prosecution from the state to make those ideals dead. Also it's still patriotic, and don't get me wrong, patriotism is still somewhat alive in the west, but it would be really hard to find a Russian, or truly anybody in eastern Europe who doesn't still love their country, unlike the west where you have rows of rows of people who would sell their country to middle easterners and west Africans, which they did. I'm not from Russia, I'm from a country that's been nicknamed little Russia, if you really want to find me on the map, but I'm sure that, just like Russians, just like Americans, and just like my fellow countryman know, communism might not have completely destroyed the east, but if the current trends are anything to go by, the West, and especially the welfare states like UK, France and Sweden will have a hard time coming back to there original glory in one piece, only for the identity politics.
And, as a final note to all the Russiagaters. Do you really think it was a good idea to poke the bear? Ok, I'll stop with the puns now.