This is an older question, but I just wanted to add my own thoughts. I believe this is less an issue of whether it is okay to break "rules" or not, but rather what are your goals and intentions. If you are trying to master traditional harmony and counterpoint, then the comments on that forum could be helpful. It can be informative to compose with the boundaries of traditional rules, just to understand the aesthetic they created and promoted.
BUT if you are just trying to compose your own music, then the rules do not need to be closely followed. Truthfully, I think compositions that closely follow all the "rules" of music theory can be boring. But breaking the rules creates interest, and composers have been doing it for hundreds of years, including Bach, Beethoven, Debussy, and especially modern day composers like Philip Glass and John Williams. So ask yourself: are you trying to learn how to follow the rules? Or are you trying to compose your own music?