As with many heated discussions I have seen, there is an underlying semantic issue here -- in this case, what does the word "rules" mean in the context of music? Several of the posters alluded to the semantic issue, but lotuscent came closest to explaining it.
In the context of music, "rules" simply means "cultural conventions". Different musical styles incorporate different conventions, and these conventions can different hugely from one world culture to another. Within a specific world culture, different genres tend to share certain rules (e.g. a 12-note scale), but may differ considerably as to the other rules. So the rules encapsulate certain cultural expectations, but that doesn't mean that songs that follow the rules are "good" and songs that violate the rules are "bad".
If you are intentionally trying to write within a genre, then it is extremely helpful to be familar with the conventions of that genre. After you know the rules, then of course, you may elect elect to break them -- or more likely, stretch them a bit. By violating the rules only slightly, you can give an interesting edge to your song while still remaining within the genre. Over time, this pushing of the envelope leads to evolution in the conventions.
Conventions are not necessarily a restriction on creativity. Many creative people enjoy the challenge of working within a rule system -- perhaps not all the time, but at least sometimes. Many a classical composer has elected to follow the strict rules of a symphonic structure rather than simply writing a free-form fantasy. Poets have gladly tackled the rigid structure of the sonnet -- but that does not prevent them from writing in other formats as well.
Still, there is a lot to said for creating works that defy all conventions -- if you don't mind that there won't be much of an audience for it! Sadly, most people need to stay in touch with the familiar, and not deviate too far from it.
