The chant Down with America is often a softer translation of the Persian saying ( مرگ بر آمریکا) which more directly translates to Death to America, a saying that commonly is used to show discontent for the government of the United States. The term generally does not refer to the every day people of the United States or the Americas, but instead to the government and polices in the US which cause harm.
The term “Down with” in general is pretty popular in some protests and means that something is bad, and that you want it to fall and fail. The same thing can be said about the US Empire, which is already starting to crumble such as with the withdrawal of the US from Afghanistan and many other developments against the West. Had the US Government not involved itself into so many conflicts, they would not be so disliked. It would be great to put an end to all the horrible actions of the United States and instead try to solve their own issues. We have no problem with a prosperous United States so long as that prosperousness is achieved through ways, which does not violate the rights of others, including the people who live in the US, and so long as they also do not use their prosperousness to do the bad things.