If you don't know how something works, do you assume it is magic? Why? It's a wildly irrational assumption to assume that it is magic rather than assume absent evidence to the contrary that it works according to known physics.
Well, that's essentially a logical tautology. Everything works according to the known laws of physics but it's certainly true that everything must also work with unknown laws of physics because of basic human ignorance.
No it is not. The argument is that absent any evidence of the existence of such unknown physics happening in the brain the most logical assumption is to assume there isn't any, rather that presuming the existence of something we've never observed any hint of.