The Principle of Contingent Causation: The Impossibility of Infinite Regress.

[GrandizerII]

In a way, MWI is evidence-based. According to some cosmologists/astrophysicists, it is the best explanation of the observations at hand. It's certainly not emotion-based.

You are conflating the multiverse with many worlds.  I blame Marvel / Disney.

I'm talking exactly about the MWI of quantum mechanics. And MW is a form of multiverse.

Many worlds simply asserts the universal wavefunction has components that evolve into non-overlapping regions of phase space (via decoherence), where, for example, Erwin's poor cat is dead and Erwin sees she's dead, and another trajectory where the cat is alive and Erwin sees she's alive.

Yes, parallel worlds. How is this not a multiverse?

Among many problems with that, the biggest one involves the conservation of energy.  If both branches are real, then you've manufactured energy from the void.

Maybe, can't say I'm qualified to address this one.

The next biggest problem is how to recover the Born rule.  Suppose the wavefunction yields a probability of 0.7 for spin up and 0.3 for spin down.  In every measurement, the universe only splits into two branches. one for spin up and one for spin down.  At the end of many such branchings the universe does contain an experimenter who concludes the probability is 0.7 vs. 0.3 but that case will be atypical, do you see?  A random sampling of branches would be overwhelmingly populated with experimenters who concluded the probabilities were 0.5 and 0.5.

Again, I don't know all the intricate details of MWI to address this, but I can have a think about this and get back to you on this later if needed.

But at the moment, I'm more interested in discussing further the question of contingency of the universe, not which interpretation of quantum mechanics is the best account.