When you get a paranoid murderous psychopath like Stalin in power, "rationale" may be stretching it.

But I think it went something like this. Marx was "scientific" - Marx had created a "science" of economics and sociology, and it was the official truth of the USSR. If some crank could show that his crackpot theory of agriculture was the logical consequence of Marxism's established truth, then it too had to be the official truth of the USSR. The science was settled; all that was left was for everyone to fall in line and implement it. Anyone who opposed that was both unscientific and unpatriotic.

Except the science was objectively wrong, and implementing it resulted in disaster.