The problem with this logic is that if 80% of the salmon in the water are sterile, then the probably of a fruitful mating is only 20% of the previous rate. For most wild populations, this is cataclysmically bad.
It works on screw worm flies. It will have a similar effect on wild salmon.
Philosophy is about logic, Science is about hypotheses. Salmon male sneak near couples mating, but first you need this extra male to survive to be able to do that
What I mean is that Biology is not simple. Things that you assume to be bad, may have also a positive side. You will never know until you do actual research and, unlike that five minutes read in a newspaper, finding the truth takes years of serious work.
Unless you spend many hours studying, you may never notice that 'kelp' forests are changing even in places without salmon farms. Without a single salmon farm, Spain lose 90% of their "kelp" (in fact Laminaria) forests in the 1990's. So maybe there are other hidden reasons for the change?
After years the ecologists understood that the problem with kelp was the sea temperature raising just one degree. This was enough to lose thousands of Km of submarine forests around all the North coast of Spain in just a decade. A good example of collapse of the entire ecosystem after minor changes.
Without spending hours studying, you may not realize that kelp war against green algae lasts for millions of years. Kelp evolved to be one of the fastest growing things alive and to build chemical defenses. If algae has the upper side suddenly, maybe there is more to see than the simple answer of "is contamination". What prevents kelp to use all this extra nutrients to grow instead?
Biodiversity is the biggest and more complex machine built in this planet, and tends to do unexpected things. Ideas like "monogamy: good", "cannibalism: bad" are useless in biology. Biology does not care about moral stances or tables of the law, and not always act as ideology would wish
It works on screw worm flies. It will have a similar effect on wild salmon.