The thing is that culture, motivations, and technology are all shaped by constraints imposed by the laws of physics, which (by definition) can generally be presumed to be universal. Having plausible explanations for "why so" doesn't change the fact that doing so would likely be so inefficient that it would place their entire culture at a significant disadvantage.
Yet on a cultural level, I think the "food/slaves" narratives of alien invasion are actually failing to be open-minded enough. Mechanical labor and physical nutrition are the kinds of things that our newly industrialized post-colonial societies worry about. It's not actually a particularly "alien" idea. Thinking a much more technologically advanced society would come to Earth for the same reasons comes across to me as projecting our own anxieties and sins.
Yet on a cultural level, I think the "food/slaves" narratives of alien invasion are actually failing to be open-minded enough. Mechanical labor and physical nutrition are the kinds of things that our newly industrialized post-colonial societies worry about. It's not actually a particularly "alien" idea. Thinking a much more technologically advanced society would come to Earth for the same reasons comes across to me as projecting our own anxieties and sins.