..so you can see that different people, nations, cultures have different conceptions of what is right and what is not,
That is true. In some countries you can be shot for criticizing the government. However, this trial and this website are in the U.S., so U.S. laws apply, even to people commenting from outside the U.S. So, you should feel free to say that Rossi is a scammer. Libel laws do not apply. He is, manifestly, a scammer, and truth is a valid defense against libel in the U.S.