No, not the social agenda driven coverage issues like you mention, but the "please my constituents" based coverage mandates. Members of congress have every incentive to maximize coverage and minimize rates to show they're "fighting for the hard working men and women they represent".

That's great, but increased coverage needs to be paid for. In a private model, if a company decides to include generous health benefits (low deductibles/co pays, low out of pockets, non-standard coverages...e.g. sex change operations, breast implants, etc) in its group plan, either the company, the employees or both, will have to pay for the higher coverage through higher premiums. So people choosing the coverage options bear the cost of those decisions. With single payer, congress can (will) just mandate stuff without worrying about paying for it (see part B, Medicare as an example). Unfunded coverage mandates will just go as another deficit item. Or congress will continue to increase the ACA surcharges such that a relatively small portion of the population gets stuck with the bill to pay for Congress's generosity.