"Socialism in one country" gets distorted. From 1917 to 1949, the USSR was effectively the only country socialist country on earth. A policy of isolationism was necessary to survive and build socialism where it stood a chance. In my experience, Trotskyists argue that the USSR was on the wrong side of history from the minute Lenin died: refusing to join a popular front against fascism, agreeing to non-aggression with Germany (after being rebuffed by the West), and then (most bewilderingly) for joining a popular front against fascism while Nazis were waging a war of extermination. The USSR came out of the war stronger, and the second war of imperialists against one another led to successful revolutions worldwide.

I personally think Trotsky is pretty cool. He's a talented writer and a certified badass who helped win the Revolution. A historical materialist analysis of the revolution suggests that history wouldn't be that different if Stalin were replaced by someone else. Social movements and material conditions matter a lot more than individuals. So Stalin wasn't some "diabolus ex machina" that ruined an otherwise perfectly good communist revolution. A lot of Trotskyism in the West bears the imprint of liberal squeamishness about the brutal reality of (anti-)imperialism and building up productive forces. As others in the thread have mentioned, Trotskyist sects are prone to infiltration, splits, and being co-opted by global capital. I will still call them comrades though: it's not like we have enough power yet for these academic differences to have any real meaning.

EDIT: Not to do a gratuitous idpol, but looking worldwide, "Stalinist" MLs tend to be a lot less white for historical reasons that should be obvious. Several prominent neocons started out as Trotskyists. Something, something, Western-chauvinist narratives.

EDIT2: Damn, I forgot about Yugoslavia and Albania when I said the USSR was the only socialist country. So from 1917-1941, at any rate.