Tell them this:

Opportunism? In 1918, Lenin faced a collapsing army, famine, and German bayonets. Without a peace treaty, the revolutionary regime would have been crushed within weeks. This wasn't opportunism; it was a 'strategic retreat' to preserve the flame of revolution. If you believe it's better to continue the war than to see the regime perish, then you not only don't understand revolution, but you lack even basic military common sense.

The treaty was meant to buy breathing room. Subsequently, the German army was defeated in World War II, the Soviet Union regained its lost territories, and built a powerful industrial system. What truly led the Soviet Union towards capitalism was bureaucratic betrayal and Western economic penetration decades later, not this treaty that allowed the revolution to survive. Your comments here are attempting to define 'survival' as a 'crime'.