I think it is and was very irresponsible to poison a whole river system at the detriment of maybe thousands of species just to save one or two species of fish.It has to be remembered that the vast majority of people dont really care about Salmon or fishing, but many might care about birds,insects,plants or animals that rely on the rivers,so i think that most people (me included) would be against the poisoning of any rivers.I don't think GS can survive full salt water so that isn't a problem. I think it can be spread by wildfowl and that could be very serious.
The big problem with GS is its a very slow burn. It can take 10 years before parasite levels reach a point where they cause mortality, then suddenly all the parr die. By this time it will likely have been spread far and wide. There is no cure, the only way is to poison the whole river and start again. I'm sure our Norwegian correspondents will tell us how hard it is in practice to eliminate.
It is the responsibility of any fishers going abroad to fish or any coming here to make sure their gear is clean.
If febs can indeed spread G.S. then there is another reason why they should be culled.
The best cure for G.S. is prevention.