I guess I will be the one to disagree. I have my hair thinned with a razor pretty regularly and I have no bad effects from it. My stylist goes through sections in the back with the razor. We don't take alot off, just a little here and there in the underneath part. We usually do it every other appointment. It works well for me because my hair is extremely thick and it gets weighed down pretty heavily in the back so by razoring it I am getting a bit more bounce but not as much fullness which gives me a better style. We also do a couple spots on the sides because they get really bulky but that is not done nearly as often. It is really just the back that I have trouble with.
Now thinning shears on the other hand are just plain evil. I have never had good luck with those.
Hair Type: mix of 3's, growing out an angled bob, color-treated red.
Current products: GVP conditioning balm for co-wash and leave in, Curl Junkie Curls in a Bottle, Pattern Pusha and Garnier Anti-humidity hairspray
Hair idol: Kimberly Schlapman from Little Big Town