This is my read of it, I don't really have any special data about the average voter, so feel free to disregard my opinions.

I think the objection to datacenters is not really an objection to the physical buildings and side effects thereof. Like you say, there's not that many downsides to most of these projects.

I think the objection is that people feel like the world is spiritually messed up. Our system's response to these people is "we have AI now, and that's actually going to accelerate things. It's going to be just like today, but moreso! Don't you want that?"

At some abstract level, people don't like the direction we are going in a very broad sense. The fire of modernity is nice to warm you up, but when it gets away and turns into a blaze, people realize that there's something gone wrong.

That there are so many concrete objections trotted out, and that people switch between them at will -- that tells you that people do not like it, but they are having trouble articulating why. Which is fair. It's very difficult to articulate. But people do understand that AI, datacenters, computers, etc are a cause. It's because they are a physical thing. The physical totem of the spiritually bereft online world that big tech has created. It's the online AI slop world people don't like; the physical manifestation of that world is the thing they can concretely object to.