If you don't believe in anything metaphysical then good and bad are still statements about the human brain. If you really committed to materialism, you could keep going as an English professor but you would have to start explaining things in different terms.

If anyone was willing to do it, "this painting is beautiful," could be put on exactly the same footing as "this drug cures clinical depression."

I think you mean redefining "this painting is beautiful" as "this painting makes me feel good." Not the same thing.

That depends on your definition of "beautiful".

Sounds like you agree.