It doesn't, what he is saying is that the companies that do crash and burn after revealing salary information to their employees are the ones that should crash and burn. There is not an inherent evil in paying a lower salary. On the other hand,if the only reason they are able to pay a lower salary is because their employees do not know any better, they are more likely to be negatively affected by opening their salary information.

I didn't read it as a moral judgement.

The important characteristics of the companies he's talking about is that they're in an unstable equilibrium dependent on wage ignorance. Meaning that wage info itself would destabilize them rather than any of the mentioned toxicity.

I think he's excluded "companies that underpay but are stable in the presence of wage info" from the class that "should [be expected to] crash and burn".