1. It's a big difference whether you live in an unjust system and individual terrorism is the only recourse you feel you have left, or whether you are the leader of a massive bureaucratic state that has other options.
2. There are numerous reasons to be mad at Stalin, and offing capitalists is not one of the top ones.

• Betraying everything Lenin and Marx stood for by bolstering the bureaucracy instead of abolishing it (admittedly partly also the fault of the German social democrats).
• Abandoning the idea of world revolution in favor of his brain dead socialism in one (technologically and culturally backward) state that didn't have the material conditions for socialism in any way, shape, or form.
• Collaborating with the Nazis at the beginning of WW2.
• Smothering nascent revolutions like the Chinese one, sending many of them on a one-way track back to capitalism, and constructing undemocratic bureaucracies like itself.
• Killing soviet democracy.
• Rolling back on the social accomplishments of the October Revolution (e.g. abortion).

This is by no means an exhaustive list.

One difference is that we are 100% certain Luigi did not even accidentally kill one single innocent person.

It's not a double standard though. Killing one person who was objectively profiting off of the lives and suffering of millions of people is very different than killing/imprisoning anyone who disagrees with you.

Luigi had the courtesy to allow the witness 5 feet from him to go about her day. He knew who the real problem was.