This point was, AFAIK, not addressed in the earlier thread.

I expect that Southwest is not displeased when people who are large enough to overflow into the adjacent seat but who are nevertheless unwilling to make use of Southwest's generous refundable second seat policy decide to fly another airline. The other airline's lack of an explicit policy does not eliminate the problem, but as long as the passenger flies another airline, the problem is not Southwest's.

Southwest has obviously run the numbers and concluded that they will lose fewer customers with the current policy than without it. The complaint ratio is solid evidence that the issue cuts both ways, and Southwest has decided to stand up for the right of all passengers to have the space they paid for.

I would prefer airline seats to be wider, but the reality is they are going to stay the way they are for a long, long time. I doubt the traveling public would want to pay 10% more for 10% wider seats even if it were possible (which it is not on a current narrowbody aircraft).