It is very easy for anyone to say, of something complex that he does not understand, or will not take the time to master, (e.g. Calculus, Relativity) that it is rubbish (or stronger). That does not make his statement true!

Why should improvisation be "instinctive" - are we all born with an instinct for harmony? No, it is learned, either formally (from books etc) or informally (by listening to others).

The 'theory' is there so that we can pass on the acquired knowledge to others.