It's really a question of scarcity versus abundance.
In a truly AI-optimized world with viable robotic replacement, in its end state, there should be an abundance of food, an abundance of clean energy, an abundance of anything humans could possibly need. So there will be no need for money, no need for economic systems at all. There's plenty of SciFi written along these lines, and also a decent amount of Sci-Non-Fi exploring the possibilities.
The problem, of course, is the intermediate state. The state where there's not yet abundance and yet humans are displaced and replaced by AI and robots. That's where the uncertainty and apprehension sets in. How are we going to get from here to there, and what's going to happen to us in between?
All of this of course presupposes that the AI entities are allies rather than enemies...
... but I've already talked at length about my feelings on that, and why I'm optimistic that we'll be okay in that regard at least.