To me and most of the people here, no. To some, yes, it does. But the only reason it does kill their creativity is because they treat theory as a box, essentially suffocating their creativity in the long run. But as soon as they open that box and let in fresh air, like the imagination, then creativity can start to breathe again. I have a friend who kept his self-taught theory knowledge as a box, but he's now starting to realize that opening the box and bending the rules can benefit you greatly after watching how I approached one of his projects.
There are also people, like MetalRenard, who don't need a lick of theory to understand to be creative. They simply let the natural musicians in them to take over and create great music. And I feel like these people need to be recognized and respected as well. I mean, why is it that I feel like not knowing theory is treated with such hostility in the music world sometimes? Sure theory can help with understanding of why things work and what works with what, but I honestly don't feel like you need it if you've already got a gift for music and aren't curious about how theory fits into it all.
Speaking of a musical gift, not to toot my own horn here, but I kind of want to talk about myself. Now I was born into a musical family, everybody (mainly on my mom's side) having been in music one way or another. So growing up, I was able to pick up some theory from listening to my mom play the flute and watching the notes on her sheet music, reading one of my grandmother's piano lesson books and plucking out songs. All throughout school, I was in Choir, so my ear for music just kept getting fed as my knowledge grew, even more so by voice lessons. But until I got FL Studio, with it's great piano roll to doodle on and some great tutorials on Youtube, my creativity was nonexistent and I don't think I would have ever been able to make my own original music, let alone make trance. Now when I write, I don't need to think about theory or really even put it to use intentionally, my mind and ear have grown so used to the way music works, certain keys, which I can pluck out no problem and create a song in that key, and I was just well, born with it. Sorry if I seem braggy, but there are some people, like me, who don't know advanced music theory but understand it, and are intuitive and talented enough to be able to write music without formal training. We may not know what we're doing half the time, but what we do know is that we're creating music, and it's something a lot of us love, so don't stifle our creativity when you find out a good musician doesn't know theory.
Wow, didn't mean for that to turn into storytime/rant. Whoops, sorry.
It depends on how you treat theory, honestly. You don't need it but sometimes you do. Every musician's different and you need to find out what works for you. Need theory? Great. Don't need it? Good for you.
As long as you create good music, you earn my respect.