I think those articles just show the authors didn't want to think a bit about all the direct effects.

Sure, by boycotting a business, the workers of that business (may) see their paychecks lowered. But the workers of the competing businesses where you'll be eating/staying instead will have more customers.

In fact, by going to that business instead of the one you'd go if you were boycotting the first, you are in fact doing the same to the later business as the boycotters are doing to the former.

So I can see how the boycott might be bad for the workers of the boycotted business, but it's neutral to workers in general.