When you sign up to work for the company, you agree to do X and they agree to pay you Y. You are disloyal to them if you don't do all or part of X (for instance, if X includes thinking up ideas for them, taking your really valuable ideas that you thought up while working for them and leaving and using them yourself), and they are disloyal if they don't pay you Y. Those are the terms, after all! So I don't see how loyalty only goes one way...