The best way to preserve cultures is in museums.

Otherwise, cultures are dynamic things that change continuously. The US "culture" is particularly dynamic because of how many immigrant groups have influenced it over the past 200 years and how many new immigrant groups continue to add to it. Imagine the world rejecting cell phones and their impact on culture because it was an American invention... how about PCs, another American invention which influenced culture. Even more basic blue jeans, invented by a Jewish immigrant tent maker who saw an opportunity to sell pants to gold miners... which culture do blue jeans belong to... Jewish culture or American? And should other countries be prohibited from wearing them?

The silliness surrounding cultural appropriation has risen to the inane levels. There is a huge difference between adapting something from another culture to your use because you admire it or find it helpful versus mocking another culture.

The former is complimentary the latter is offensive.

If anything, American culture is the definition of cultural appropriation.