These are just some of the considerations that lie at the heart of any defense of unions, regulation of contract and the workplace, and workplace democracy. Whether we call that defense egalitarian liberal, social democratic or democratic socialist, libertarians reject it as an abridgment of economic freedom and, more particularly, the freedom of owners to do what they wish with their property. But the defense of freedom requires such interventions. Private power, left as unrestricted as the Bleeding Hearts would leave it, simply gives too much scope to private empires of tyranny and domination. Taking freedom seriously means confronting the unfreedoms that ordinary people are subject to in their ordinary lives: the Bleeding Hearts, with their fetish of private property and contract, just can’t do that.
Basically, Bertram, et al argue that if workers only have the exit option, they will be enslaved by employer-tyrants. However, if they are given the voice option, through unions and government, they will enjoy freedom.
Whether their argument holds depends on how well the options work in practice. By “works well,” I would focus on consequences.
Just be careful about assuming that there must be a perfect option. For example, if the exit option is imperfect, that does not mean that the voice option works perfectly.
My own view is that neither option is perfect. However, I think that the exit option tends to work better, and that adding the voice option, whatever its merits might be in theory, tends to be detrimental in practice, particularly if one takes into account the effects on third parties, notably consumers and unemployed workers.