Is it more unethical than any other entity selling consulting for CentOS and Red Hat support?
Obviously this is entirely my opinion :-D
There's also an impossible-to-measure factor in the form of eco-system benefit though. For example, I would never have paid for RHEL had I not entered into the eco-system through Fedora and CentOS. So while RH didn't make money from my CentOS usage, it did eventually make them money because I bought RHEL later when it was worth it. I don't know how you would calculate that, but it does offset ethicality deficit somewhat as well
That said market competition in general is a good thing, and I don't doubt for a minute that Red Hat prices would be a lot higher without the competition. It's a complex equation that's impossible to calculate since the inputs are immeasurable and in many cases theoretical.