There are two types of environmentalists. The first type is genuinely concerned about protecting the envrionment. They are generally reasonable but sometimes fail to realize that everything has tradeoffs, and maybe saving a particular species of insect isn't worth thousands of jobs. The second type are utopian socialist luddites who care about the environment only as a means to attack capitalism, technology, individual freedom, and pretty much everything Western civilization stands for. They won't accept any source of energy that allows us to maintain our decadent materialist lifestyles. Nuclear power is objectively far better for the environment than fossil fuels, and thus a convenient way to tell the two groups apart.