Do you notice that the comparison was used to justify real slavery?
So? There is a fundamental difference between "wage slavery" and slavery. "Wage slaves" can always choose to leave and find some other way to feed themselves, whether it's becoming an entrepreneur, finding a better paying job, etc.
Yes, finding a new job when everything you're qualified to do pays the same shitty wage. Sounds viable. Almost as viable as becoming an entrepreneur on a sustenance-level wage working 18 hours a day.
It's all about CHOICE, even if your choice is between abject shit and a pie-in-the-sky dream that, pretty much by definition, can only be realized by a tiny fraction of the populace.