Democrats don't think this far ahead. We all know the quality of healthcare in the US would decline if we had single-payer. With "free" healthcare, the lines get longer because people come for every sniffle and cough with no co-pay. Many come just to talk out their problems(trust me, I know this). We will need more doctors and the way to get more is to lower standards. We will also have to pay them much less because the government doesn't pay as well as private insurance. Maybe single-payer means the doctors will all be government employees and governed by them. Boy, that outta go really well. I mean, just look how efficient and proficient most government run institutions are. Said nobody ever.
Single payer would absolutely destroy quality healthcare in this country. On a positive note, it may curtail illegal immigration to some extent. No reason to come to the US for quality healthcare.