> I believe free markets do exist, and have always existed - at the highest levels of human organization.
A free market exists when force is barred. The U.S. came close to a free market at the time of its founding and has become progressively more unfree since. Western European countries (particularly England and France, sometimes Germany) have a similar but less pronounced trajectory over the same span of time. International politics is not a free market; it's a collection of armed "gangs" (effectively) that all can use force against one another. Tariffs are also a serious use of force and violation of a free market.
A free market literally just means "no force is allowed." If you don't like the term "free market" being used that way, just replace every instance in my comment with "no force is allowed." I'm not interested in arguing about the names of concepts and principles; only about concepts and principles.
Gresham's Law is designed to account for a legal tender situation where there are forms of money with the same nominal value under the law but different real value. I will quote a section from Wikipedia which I agree with:
"Those examples show that in the absence of effective legal tender laws, Gresham's Law works in reverse. If given the choice of what money to accept, people will transact with money they believe to be of highest long-term value. However, if not given the choice and required to accept all money, good and bad, they will tend to keep the money of greater perceived value in their possession and to pass on the bad money to someone else." [1]
I mean, we don't need to trust Wikipedia to see this. People prefer to use the most liquid token of exchange for all transactions, though it also needs to be durable, fungible, etc. The most liquid "token" (and it could even be a commodity) then becomes the best store of value because it is used in transactions. There will never be a place where one money doesn't drive out the other (good drives out the less-good) because one will be more liquid than the other. The whole point of money is just to be something you can trade for anything because everyone will trade it for anything. It solves the "coincidence of wants" problem in a barter economy---the fact that if you are a fisherman and I am an apple grower, I can't buy fish unless you want apples and vice versa. Pardon me for being pedantic; at this point I've gotten into territory that you've very likely encountered before.
People would prefer a sound and honest money if there were one. Bitcoin was designed to meet these criteria if it were to become liquid enough; maybe some day it will be, or maybe not. Gold was a sound and honest money, but world governments got us to slowly get off gold, one step at a time. So now it doesn't have enough liquidity and is anyway on shaky ground legally.