Rules have exceptions, laws have not. Therefore, except from the physics laws that define how sound behaves in nature (vibration, waves, harmonics, carrier etc), music is a human art and not a constant in the universe. Therefore, "laws" in music are irrelevant by default. If something (anything, from tuning to forms) is mostly used, consider it more like a rule that could have exceptions (exceptions that could even be created for the first time by you) than a deterministic law. In other words, do not feel "chained" by all the theory that you learn here or everywhere.
Defining art could be this: Art is a form making process. The material, though, can be "abstract". Poetry uses words as a material, while sculpture uses real resources. An artistic person has a talent of form making. Arts in general are close to the purpose they are created for. Pottery, for example, is an art of making storage devices for common goods and a good product would be evaluated according to form as well to service quality. So, Pottery is depended by practical rules.
But arts have a significant distance from fine arts. As fine arts have a more "abstract" purpose, the main concern is the form itself and not practical issues by any means. Fine arts have therefore full control over rules, and rules themselves exist to serve these arts, being music, dance, painting etc. That's why, in fine arts, we see more often rules to be questioned, substituted or completely overriden by others. There comes a time when the "exceptions" take over the "rules" themselves as the main purpose is to evolve. So, when you write a modern piece and you are "tortured" by those parallel 5ths, remember Henry Manchini's "Pink Panther Theme" that uses them brilliantly. This issue would be completely different if you wrote a stylistic exercise. But talking mainly of composition here, always remember that rules serve your art, and not vice versa.