I get you think that, but consider this
how much volume of bitcoin are you transacting in every month verses how much fiat volume are you transacting in every month.
Whichever has the higher transaction volume is really the one you are supporting.
I save more Bitcoin than i spend fiat, so more Bitcoin. Leave nothing in my bank and spend Bitcoin or cash when i can. I cant force everyone to accept Bitcoin or to pay me in Bitcoin when they dont want to. Its clear what im supporting, not just by the way i handle my money. Yet what im supporting and my individual actions will be meaningless, if not much more people opt out too. So its not just about me and even if i get more extreme about not touching fiat, it wont make any difference currently. Its a collective decision that determines which path were choosing in the end, i made my individual decision and am doing my part to make it possible. If this fails then atleast i have the peace of mind knowing that nothing couldve worked to fix this mess or to change something, because its people itself that refuse to fix it and that the current system was just a better reflection of the true nature of humanity.