Thank you for taking the time to tease out these differences.

Instead of killing and replacing them, they 'persuaded' them.

This is exactly what Nagare tried to do in his rooftop chat with Shiro at the end of ep.5. It sounds like they both want the same thing. In your summary:

Red and White King : Destroy the slates, so that no one has powers anymore (fair)
Green and Grey King : Spread the power of the slates so that everyone has power (either insane or brilliant, but fair)

It's fair because the outcome is the same: Everyone having equal access to superpower would be the same no one having superpowers, because we would be on a level playing field, right?

So it's fine when politics keep the current defective system, but when the Green does it, it's evil?

No, and yes. This is the reverse of the a false equivalence you used for {red and white} versus {grey and green}. The system wasn't fine. I agree with you. It allowed Kagutsu to happen. I'm painting Green with the same brush because they haven't solved the problem. They have escalated it.

Your example of gun laws is right on the money. More power is more threat.

I'm going to up the ante. The correct analogue here is atomic weaponry. Kagutsu Incident look like you-know-what. With what you are saying..well, you don't bring a gun along to fight where the other guy has nuclear warheads. This is where "either insane or brilliant" become plainly "insane", and there isn't any "fair".

The Gold King spent his life to minimise that harm. Munakata was also willing to shorten his own for the same reasons. It was as futile as holding back the tide. The Slate still activate Kings and Strains. Surely then, this is the same as Nagare's free for all, if Kings and Strains are also activated? No. It's the path that leads to the outcome.

You are denying that the Everyman has a choice about how this world should be. Up until now, in the Gold Kings domain, humans had free will to decide if they wanted to become a clansman. With Nagare's release of the Slate, that's not true any longer. The freedom that Nagare is offering has been inverted.

So tell me why Nagare sent the Colourless King to throw the Silver King down from the sky. He didn't need Shiro around if all he want was to wait for Kokojuji to die of old age and steal the Slate.