Some of the concerns expressed are real but a few are a bit misplaced.
Hatchery fish have, in general, much fewer diseases than wild fish. Hatchery fish are inoculated and fed special diets to make them more disease resistant. Wild fish usually test positive for a wide variety of diseases and often have a heavy parasite load. So there is no direct threat to wild salmon. However, if a wild fish gets hit with a disease, it drops out of the school and generally dies. If a hatchery fish gets hit, it infects the rest of the school since it's confined to net pens. Plus, with the high densities, the disease travels quickly in nets and can inflict high mortality on the entire brood. It's possible this could have an effect on wild stocks but not likely.
There is a high likeihood that with the expansion of salmon farms, the price of salmon will drop considerably. This is both good news and bad, depending on who you are. Most consumers will think this is great. Commerical fishmen should be justifiably concerned. Sport anglers might have more to catch if the commerical catch drops because of reduced consumer demand for expensive "wild" (not pen raised) salmon. For some of us, that would be okay.
However, if the price of whole salmon continues to drop, look for the Tribal folks to increase their take of salmon strickly for their eggs. Since the price of salmon eggs is not likely to go down much with the increase in salmon farms, they may continue to fetch a high price. We've already seen this all over the Oly Peninsula with the harvest of chum salmon. The females are netted and the males are returned to the river (albeit dead).
Regardless of these factors, it's just a matter of time before Atlantic salmon (escaped pen raised salmon) become firmly established on the Pacific Coast. This shouldn't be a huge problem (my opinion) since their life history is very similar to a coho salmon but Atlantics seem to be even less tolerant of poor habitat conditions. I suspect they won't be much of a factor anywhere. But having a non-native species compete for space and resources, especially in the juvenile stages, is probably not helpful for salmon/steelhead recovery in the PNW. It's just one more thing for our native salmon to overcome.