If you've studied Trotsky you no doubt are aware of his use of the Red Army to murder innocent people. Unless, as is the case with many supporters of brutish thugs, you see past it to his more redeeming qualities.
As for being in the left opposition he went there to lead and then left others to take the punishment as he was exiled. He is as much responsible for Stalin as any person of the former core group.
The elderly gentleman said Trotsky had his followers hoodwinked, that they didn't realize he failed to believe much of what he wrote and was the intellectual version of JS.
No doubt, as you've combed through the archives, you've seen this material.