You can chose to consider that someone represents a group or not, by informing yourself and thinking critically. Moreover, refusing the principle that Trump represents all American contributes to undermining his power. Saying “the real world” means nothing, you could retort that to support any idea, it’s vacuous.
A boycott is all about seeking specific consequences. If you turn it into a rigid, simplistic stance you fail to grasp what it is. Here my point is that boycotting even powerless Americans in need of support and who are even targeted by their government does nothing to achieve the goals of a boycott, or very little, and even help with Trump’s plans. I attribute the failure to understand that to nationalistic thinking, because it’s such a simple argument. At no point have I equated a boycott to nationalistic hate. You are confusing everything with everything.