I think you're both right.
It's hard to fully blame the humans for hurting hosts when they didn't realize the effects of their actions. However, it's also true that they should have been questioning and thinking more critically about the hosts all along. They start with the assumption that the hosts aren't conscious, but their observations seem to imply otherwise. So, rather than trusting what they are told, they should question based on what they are actually experiencing. But it's such a fuzzy area, determining whether something has consciousness or not, that as I said it is hard to blame the humans for brushing off the signs.
It almost reminds me of how we treat animals. Many assume that most animals do not possess consciousness, and some see this as an excuse to treat them however they'd like. They can't feel emotional abuse anyway, right? And yes they feel the physical abuse, but is it really abuse if the animal doesn't have a conscious understanding of what it's feeling? Even if you take abuse out of the equation, we treat animals as test subjects in experiments, even though we require permission to do this to humans. The results of the experiment may benefit humans for generations to come, and the animals won't really feel it or care anyway, right?
And yet, most would agree that we should not abuse animals, and some also feel that experimentation on animals is wrong. Because, although we've been told they don't have consciousness...what if they do? Just, what if? On the off chance that my cat knows exactly what I'm doing and feels the emotional repercussions, do I really want to treat him poorly? Do I believe scientists who have studied animals and told me that a cat is not self-conscious, or do I believe what I often observe with my own senses when interacting with my cat? Am I just anthropomorphising, or are we overlooking the obvious just because we don't understand the science behind it?
I don't know. I really don't know. And in Westworld, I don't think it's fair to say that the humans should have known. But, maybe we (and they) should treat the world around us with respect and kindness, just in case...