There are a lot of different opinions about this. I think Alaska's position is largely governed by farmed salmon competing with harvested wild salmon. Prices for commerically caught salmon have been in the dumper in recent years, which hurts Alaska's economy. Low prices paid at the docks tends to reduce commerical catch effort, which means more fish for sportsmen.

That said, Norway has had some serious problems with the waste from salmon pens polluting some of the fiords, so it's apparent that salmon farming is not without it's impacts.

I'd love to read an objective study of the pros and cons, if anyone knows of one.