Keep at mind that any person in different, and any CFer is different. Some may eat normally without problems. I couldn't. I didn't give up on all the food I enjoyed because I'm mentally unhealthy (!) but because it did make me feel better.
My "chicken-rice-yogurt" diet surely is not balanced. Yet it doesn't mean it is "bad". I am still followed by my doctors, and my BMI is almost perfect, my lung function is stable in the 80s, and I feel better.
Something that, I am absolutely sure, would be different if I would be on a balanced diet.
Surely I could eat more veggies or fish, but I simply don't like that. Yet it's now been months I've been going on like this, my weight is stable, I am not malnutrited and my health, physically, improved. As for my mental health, while stressing, I carry on because should I stop it, I would feel way more sick than I do now. At this point I just can't step back, it would be masochism.
I perfectly udnerstand the point of those who can eat fine and be good with that, just try to understand that not everyone is this lucky. Not for that you should judge in such ways, in my humble opinion. I already fight with my doctors about my diet, and yet I have a simple, effective fact on my side: I feel better (much less mucus production, and I mean very little to none), I have less CF episodes of any kind, and my nutritions values, my look and my BMI are fine. I even managed to put up some muscles with just rice and chicken.
This said, if ever will come out an effective Vertex drug for me as well and it will fix my guts, I'll be extremely glad to be back on a normal diet.