Everything that you eat destroy the environment in one way or another. Social license means nothing when people need to eat, need jobs, work, some form of income. Would you be prepared to let go of your income in order to feel good about the environment? Obviously not. Tassal corporate responsibilility is in the how much hundreds of millions of dollars revenue it brings to Tasmania. That has a massive knockon effect on the local economy.
It is not like Tassal is not doing anything they improve, in fact they are investing in a lot of different things into the near future not limited to seal proof pens, waste capture system, co-cultivation of seaweed, etc. It is just that people are mostly fundamentally narrow minded and stupid and tend to ask too much without providing any form of a solution, stupid people want a cake and eat it too.
Tassal, Huon, etc is about as good as it gets by world standard and as far as aquaculture go that is about the only way people can eat fish in the very near future. It is worth investing because Tassal and the likes are the future. Wild caught would be just too rare and too expensive to be profitable let alone affordable.