I think it’s partially a generational thing — people in the US who fought the “no nukes” fight in the 60s/70s and remember Three Mile Island (or saw Silkwood), are instinctively opposed to nuclear energy. Many environmental groups and environmentalists come out of these battles from years ago, and therefore seem unusually hostile to nuclear energy relative to its environmental damage as compared to burning fossil fuels.

I think they’re also somewhat rightly concerned that nuclear shouldn’t be a substitute for seeking sustainable energy from wind/solar/hydro. Nuclear can be an excellent bridge source of energy until we can harness those others, but given how long it might take before we’re using solar and wind for our energy needs, nuclear would be a far better option in the near and medium term than continued burning of fossil fuels.

I’d also point out that no nuclear plant has been built in the US in decades, and yet they would be much safer now than during their heyday in the 70s when they were being built. A real shame that we can’t get this one right.