Atomic theory was once considered impossible to falsify, and atoms were once thought to be unobservable in principle. Evidence of a multiverse could share the same fate. Ultimately, arguments against a multiverse purportedly based on falsifiability are really arguments based on ignorance and taste: some physicists are unaware of the history and philosophy of their own field and find multiverse theories unpalatable. But that does not mean that multiverse theories are unscientific.
