Good Question! People should be aware of te downsides along with the positives.
As others have said, it does take the fun out of browsing the hair care aisle at most stores. So many things become off limits. But, as better silicones are developed, I think that fewer people need to go totally cone free than, say, twenty years ago. Some can handle the water soluble cones, or cones that come out with a CO wash or a Low-Poo type of cleanser.
I never noticed a protein sensitivity until after I had been cg for a little while. It got worse as I went on. I have wondered that if I went back to some sort of mild sulfate, could I handle more protein and have fewer limits on what kind of conditioners I can use.
The militancy of some cg-ers. Just because it works for some doesn't mean that everyone has to follow it the same way that a lecturing militant wants you to follow it. Everyone has to find out what works best for her.
With my hair texture, I've not had to worry about the overconditioning thing that others wrote, but it does seem to be a fairly common side effect.
Med/Coarse, porous curly.