We all know the healthcare situation is terrible but the main politicians that want to change this offer 100% government controlled single payer healthcare as the only solution. That would take us from the least socialized system in the world, to literally the most socialized system in the world.
I don't think you have to try very hard to imagine why people are uncomfortable with that.
Edit: Never make one slight error on HN or your entire point is invalid, it would be one of the most socialized by the legislative proposals, but not literally the most.