The American Southwest has horribly mismanaged it's fresh water supply. Tulare Lake, Hoover Dam, and Las Vegas are just some examples of the American Southwest's horrible fresh water management. My suggestion is does the rest of the United States and North America have a right to the fresh water contained in the Great Lakes? Would a pipeline from Chicago to Los Angeles or Mexico City be better for the environment than a desalination plant?
Or just open borders and let people settle where it makes sense. Pumping water thousands of miles to a desert is as bad or worse than all of the other water megaprojects in the desert. People shouldn't live where there isn't any water. There's a carrying capacity to everywhere and deserts are pretty close to zero without a ton of environment-destroying engineering.