This is what I took from this text:
If you're in a capitalist country and your country is at war, you can't claim to have revolutionary ideals while also advocating against your country's defeat/for its victory.
Also, wow, this part has aged incredibly well: ("Discerning reader": note that this does not mean "blowing up bridges", organising unsuccessful strikes in the war industries, and in general helping the government defeat the revolutionaries.)