No one in science demands proof. Just evidence. And above all, a theory or hypothesis that suggests lines of research.
In case you haven’t noticed, string theory isn’t accepted as even a theory, since no one can say how it can be tested. It has the status of a conjecture. Same for conjectures about why physical constants are what they are.
Can you site a high school textbook that treats string theory or multiverses as anything more than conjectures? Title, publication date, page?
And string theory is called a *theory* for what reason again?
It has the status of a conjecture.
And just whose *side* is the one proposing this non-theory?