This Stalin quote is an incredible quote – I think I'm starting to get dialectics

I mean, I knew the idea of dialectics. But I'd dismissed it as German metaphysics or the "iron laws of history" stuff that is embarrassing about 19th and 20th century socialism. I didn't see its relevance to practical politics, but look at the way Stalin uses dialectical thinking here –

"How do the Social Democratic Parties in the West live and develop? Are there any internal antagonisms and differences over principles in those parties? Of course there are. Do they expose these antagonisms and try to overcome them honestly and frankly before the eyes of the masses of the Party? No, of course they do not. It is the practice of the Social Democrats to conceal these antagonisms, it is the practice of the Social Democrats to convert their conferences and congresses into masquerades, into official parades intended to show that all is well within the Party; every effort is made to conceal and gloss over the differences within the Party. But nothing but confusion and the intellectual impoverishment of the Party can result from such practices. This is one of the causes of the decline of Western European Social Democracy, which at one time was revolutionary, but is now reformist."

He is saying that Social Democrats are fence-sitters. They see the duality but don't follow it to its conclusion. Communists like Lenin grasped each duality and resolved it. When you don't follow do this, you wind up as a SocDem, a compromiser. SocDems see the tension between socialism and capitalism, and try to please everybody.