That's certainly true. But as a GitLab user, I want to make sure they're hiring the best candidates to work on the product. Is that an unreasonable thing to want?
Any argument depends on context and in this case, none of the GitLab employees are facing minimum wage, working in hard labor conditions, or facing removal of their last chance at employment. The reality is that they're paid a very transparent amount without much negotiation hassle and they can easily choose to work elsewhere if they want to.
Furthermore while I can believe that gitlab's salaries are below the average I doubt they're below any reasonable proposal for minimum wage. If software developer salaries start dipping below what we consider fair I think the most efficient solution would be unionizing to raise the salaries for the profession at large.
Quite frankly I find it a bit obscene to conflate both these issues.