I voted yes.
I'll phrase the question in a different way:
Will applying 300+ degrees of heat to my hair damage it even though I ave a thin layer of silicone on my hair?
When thinking about it that way, it's a no brainer.
You wouldn't put that same flat iron on your thigh EVEN if you put heat protectant on your legs first, would you?
With all that said, just because you use heat doesn't mean that you can't have healthy hair. Plenty people with healthy hair use heat... however at the least, it causes minimal damage.Heat protectants aren't THAT good. How much damage you get depends on many different factors... the individual's hair, regimen, technique, products, tools...
but it's silly imo to think it's damage free. Even combing your hair causes a little damage. How is using high heat not going to do anything?