Yup, in baroque and classical it's better to play them in they way they were supposed to. Unlike in romantic music where expression is highly encouraged, when it comes to the earlier ones, the composer usually has something specific to convey. Sometimes deviating from the original turns the piece into something different than what was intended in the first place.

But if the performer's intention was to interpret it in the manner they want to, as long they don't completely turn it into something else...

I watched the 'In C' on Youtube after you mentioned it. It's fascinating how the composer managed to create it in a way that musicians stopping and starting anywhere isn't affecting the flow of music. Unlike in works during the baroque, classical, and romantic period, doing so in those works would end up completely destroying a performance. Contemporary composers come up with innovative ideas!

Our teachers were amused. They didn't scold him either, after all, it's a certified piece of music (music being an organization of sound and silence, though more on the silence part than anything else).