How would you argue against American imperialism in the 1900s?

There are many different arguments to make against American imperialism during this period, many of which were made by anti-imperialists themselves at the time. Most (but not all) anti-imperialists had primarily moral objections to imperialism, and this is perhaps the most cogent argument possible. The United States was a nation founded on resistance to empire—the original thirteen states, were colonies that fought to gain their independence from Great Britain. For such a nation to then use its power to deny independence and self-governance to peoples around the world, one might argue, is contrary to founding principles. Moreover, imperialism always carries the risk of war, either against colonial peoples seeking independence (as actually happened in the Philippines) or against other powerful nations competing for colonies. One could argue these wars, are not only immoral, expensive, and bloody, but contrary to the interests of the United States, which had managed to stay out of such conflicts for the better part of a century. Perhaps the best way to argue against imperialism in this period is to look at the critique raised by leading anti-imperialist Mark Twain, who said of American annexation of the Philippines:

It should, it seems to me, be our pleasure and duty to make those people free, and let them deal with their own domestic questions in their own way. And so I am an anti-imperialist. I am opposed to having the eagle put its talons on any other land.
https://www.loc.gov/rr/hispanic/1898/twain.html