Desalination is a blessing but it also increases the dependence of the population on technical infra for daily survival. If something were to happen to the desalination plants, that's no water, immediately (in the UAE case, for example).
Reducing dependence on technical infra doesn't always work out either; the story of the https://en.wikipedia.org/wiki/Lykov_family suggests that for any long-term attempts at autarky, N should be >6. (how much greater?)