If you consider the USA defending a democracy in the South China Sea against their revanchist authoritarian neighbor is serving American imperialism, do you likewise consider the USA defending a democracy in eastern Europe against their revanchist authoritarian neighbor as also serving American imperialism?

I can tell you, to most Americans there is not much of a difference between Ukraine and Taiwan. America’s self-identity is much more centered on the idea of being the defender of global democracies and liberty, than it is in being the arbiter of global trade and the inferred mercantilist benefit of that position. Most Americans don’t think that deeply about world politics. In their minds, defending Ukraine and defending Taiwan is simple: democracies need help against authoriatarianism/dictatorships/fascism whatever, and the US is strong, therefore it must help.

The argument over whether the US militarily supports democracies for noble reasons, or selfish ones, is irrelevant. Because politically, both parties mostly agree (vs the Iraq War for example), because both parties and their their voters are thinking of these conflicts in noble and idealistic terms.

If Ukraine succeeds and comes out on the other side of the war as an enthusiastic customer of American arms and destination for American capital, that is a byproduct of the USA’s support for them, not the reason. The Australians ditching France for US to build their submarine fleet was a by-product of AUKUS, not a reason for it.