If Uruguay can run on 100% renewable energy, the unstated implication is "The US could do it too, we just lack the political will". (As opposed to the idea that "Renewable energy is a genuinely hard problem that will take time, effort, and technological advances to solve.") The implication that "we just lack the political will" can feel like a criticism of anyone who's not maximally-environmentalist. I think that's why people are getting defensive about it.