It doesn’t. It’s part of a rosary of things people wield to stave off thinking about the topic. You can do other things besides nationalizing all care or insurance, but when you hear people talk about “open up markets to cross state competition”, or “everyone gets an HSA”, or “make insurance tax deductible/it’s fdr’s fault”, it’s rarely about the specific policy, those are liturgical texts / catechisms designed to give the impression of solutions without substance.

Tax deductibility is only a very minor reason why most private insurance is employer provided; the much larger reason is that employment is a decent way to get a reasonably distributed group (of people generally healthy enough to work) and that’s one way of getting balanced risk pool if you’re not doing community rating or a societ wide pool.

I suggested an alternative solution to the one proposed by the comment I replied to.