Well, it seems that there probably are legitimate things to consider with desalination plants.
They're not "100% win-win" or "0% impact" endeavors and people shouldn't pretend they are ven if they are the plant is the best option or the 'least worst' option.
And the organization isn't as extreme as it's made to be:
$1:
Desalination
Southern California's exploding population is going to need more and more fresh water, for drinking and home use, and irrigation as well. Currently there are 19 proposed desalination plants along the coast. Desalination, or the process of sucking in sea water and removing the salt to convert it to fresh water, might seem like a decent way to get more fresh water, but we need to perfect our water conservation and recycling efforts first. One of the problems with desalination is that the plants produce a super concentrated salty brine, which is simply discharged right back into the ocean. This discharge might create spots in the Santa Monica Bay that are so salty marine life can't survive. But some of the proposed desalination plants are an even bigger problem. They would be built at the same location as an outdated power plant, and use the same water that the power plant sucks in. Reusing things is great, but in this case the desalination plant might exempt the power plant from updating their technology. So the desalination would be the excuse that the power plant uses to keep sucking in millions of gallons of sea water each day. That's just not a good idea.
Heal the Bay’s position on desalination:
We are following the issue through proposed local desalination facilities and the State Water Resources Control Board's desalination policy development process. As an organization, Heal the Bay is not against desalination. We believe that water conservation and reuse should be maximized before energy intensive desalination is pursued. If desalination plants are approved, Heal the Bay believes that they must use the best technology available to minimize marine life mortality and keep water quality clean.
http://www.healthebay.org/about-bay/cur ... akes#desal