Once again this is one of those topics where it is about TECHNIQUE and common sense....
Yes BOTH can be damaging and BOTH can be great ways to obtain a straight style. Pinkskates uses a pressing comb, her hair is amazing. We have other ladies here who blow dry, me included, and our hair is fine. I have 4a relaxed, fine, hair that has about an inch or inch and a half of NG from a 2.5 month stretch. I'm sitting under the dryer in a long DC prepping my hair for a blow out.
I don't use pressing combs because in my experience its extremely damaging. Then again when I was using it I had no idea of how to use it. In fact, I used it sooo hot that one day it was on the floor - idiot - and I accidentally stepped on it and had a 2nd degree burn on the bottom of my foot that took months to fully heal.
I now prefer blow-outs to flat ironing when I want my hair straight because my hair feels HEALTHIER after. Knowledge is power. Before you use any of these methods you need to DO RESEARCH on how to properly use them, what tools you will need, and what products will work best to get the desired result. With youtube and other resources, you can put yourself through a virtual beauty school lesson and come out with the tools to doing it properly with MINIMAL to NO damage. Most people here who are dead set against these tools probably don't even know how to use them properly anyways which is why their hair feels like it's dry and breaking. For instance when you blow dry the hair, you MUST actually position it to travel DOWN the hair shaft and it should be at least 6 inches from the hair. You can use a LOW heat setting and still get good results if you use the right brush and products. So it's things like that that produces the RIGHT results, and will lead to less damage with the hair. If you need to turn up the heat to all high heavens to straighten your hair using the blowdryer, perhaps that isn't the best method to straighten your hair and you should try something that works, it's not worth it. So again knowledge is definitely power.
The pic in my siggy below is from a low temp blow out, and I was 2 months post relaxer in it.