Yep, CF sucks and there's no way around that. Sure there are folks that lead relatively normal lives but there are also 10 years olds dying from Cepacia. Explain that! You can't no matter what religion you subscribe to. It's just the roll of the dice. I'm past trying to understand it. I just take everyday as it comes (good or bad) and try to find the positive in it. Sometimes it's tough but eventually I get there.
Obviously, there is no right or wrong answer/opinion here. Hopefully, someday, we will all know the truth. In any case, it's okay to feel bad about God, Satan, yourself, you parents, the world, etc... once in a while. It happens to everyone whether they have CF, cancer, MS, or are just having a really hard time in life. The important thing is to remember that no matter how bad it is or how bad you feel, that you are making a difference in this world. That's why we're all here, whether you die at 2 or 92, you will leave your mark. Make it a good one.
People will sometimes forget what you said. People will usually forget what you did. People will always remember how you made them feel.