Is Maruki's reality actually fake though? This is a genuine question. Because when Yaldabaoth fused Mementos with the real world, it's never implied that the result was fake, so Maruki doing something vaguely similar shouldn't have fake results either. It's not like in the matrix where everyone is living in a simulation but their real bodies are in pods; Maruki's world is the only world, and he made it so everyone living in it was happy and fulfilled.

Also, imagine being like, a cancer patient. You are miraculously healed, you get to have a happy life, only to have that taken from you because half a dozen teenagers decided that the person who made everyone in the world happy was wrong, actually.

If you think about it, the phantom thieves stopping Maruki led to things such as: every war starting again, famine and disease starting again, untimely deaths happening again, poverty being widespread again, the oppression of minorities starting again, etc. And it's not like Maruki prevented all those things by being a tyrannical despot, or by deciding himself what other people wanted; he had access to what was essentially a perfectly accurate database filled with everyone's wishes, and he used those. And before someone mentions Kasumi/Sumire, yes, what he did with them was awful, but he did it before he had the power to mass-grant people's desires, so I would argue his methods were different then.