The image attached portrays the defence of Stalin as a waste of time at best, this is frankly charitable compared to most self proclaimed leftists who think the rehabilitation of Stalin is actively harmful towards our movement.
There are reasons as to why the rehabilitation of Stalin is indeed an important issue and not just some trivial thing that we must halt in order to gain a larger following.
The rehabilitation of Stalin's image is less about the rehabilitation of Stalin as a historical individual and more about defending and upholding Marxism.
Condemning or even refusing to uphold Stalin to at least some extent is equivalent to fighting our enemies on their terms. Why would we let our enemies decide who we should love and hate? There's no reason to allow the historical narrative that our enemies have constructed to be our historical narrative, that's just ideological surrender, may as well become a liberal at that point.
The total slander and demonization of Stalin's image is what leads most people into deviationist tendencies, tendencies which are totally harmless towards the bourgeoisie. It's only logical, if people believe Marxism-Leninism led to practically 1984 in real life, then why would they follow it?
Rather than keeping quiet about the USSR under Stalin, it is our duty to defend this period against the reactionary slander laid upon it. It was the first time in human history that mankind entered the socialist mode of production, and that's something to be cherished.
The number of "executions" is actually the number of sentencing, and we know people were acquitted of the death penalty on numerous occasions. The purges were a genuine response to real infiltration, and were popularly supported.
Regarding the deaths in prisons, a huge portion came from starvation, during World War II when the Nazis took Ukraine, the soviet breadbasket. The soviets were not oppressing people en masse.
"Dekulakization" was the collectivization of agriculture from the hands of petty bourgeois tyrants that often enslaved the peasantry. This was a necessary step forward, and would have been fully peaceful if the kulaks had allowed it to be.
What you are looking at is bourgeois historiography. In actual fact, Stalin was a more collective leader than his successors, such as Khrushchev. Stalin attempted to resign on no fewer than four occasions, and was denied each time. A cult of personality arose around him against his wishes precisely because he successfully solidified socialism in the USSR and helped defeat the Nazis in World War II.
Stalin was on the whole more good than bad, which is why rehabilitating him is not whitewashing. He made mistakes and there was excess, but this is going to be true regardless of who it is building socialism.