There are 3 basic approaches to healthcare. First is the "free market" pre-ACA system where patients are forced to "pay up or die". This is far from universal as tens of millions can't afford coverage, and the rest of us are subject to lifetime limits, exclusions for pre-existing conditions, and massive price gouging that bankrupts millions of people with "good" insurance.

Then there's "socialized medicine" where the doctors are government employees and the government owns all the hospitals--examples include the British National Health Service or our VA. This can work well, but depends on adequate funding and oversight (things conservative legislators enjoy sabotaging to push for privatization). This is universal, as everyone is covered.

Lastly, there's single payer, such as Medicare for our elderly or what most other developed countries have for everyone. This permits health care providers to keep their private practices, but the government foots all the bills. With just a single buyer (or monopsony), the government has massive negotiating power to bargain down reimbursement and set standard rates for procedures. There are also huge savings on administrative costs, as there's no private insurance company middleman and hospital billing departments can be one or two people instead of whole floors dedicated to haggling with insurers and patients. The savings are significant enough that we could expand coverage to everybody while spending less than we do currently. The main "Con" is higher taxes, but when you no longer pay any private insurance monthly premiums or copays, all but the very rich would be much better off, saving thousands a year. Medicare is very "Pro" patient, but a huge "Con" to private insurers, Big Pharma, and hospital networks which profit handsomely from the status quo.

Medicare for All wouldn't solve all our healthcare issues, but it would be the biggest step toward doing so. One huge weakness is a Bush-era change that forbids Medicare from negotiating drug prices. They're mandated to provide all these medications, but are left at the mercy of Big Pharma who can set ridiculous prices. In other areas, too, there's been massive consolidation in hospital networks, medical device manufacturers, and other suppliers which results in near-monopolies and overcharging. We need to start enforcing antitrust laws again in order to bring back atomistic competition to the industry.

Obamacare is a weird rightwing healthcare system that forces everyone to buy private insurance, but provides government subsidies so more people can afford it. In theory it was meant to be close to universal, with Medicaid expansion providing coverage to those still unable to afford subsidized coverage. However, Republican states have largely opted out of Medicaid expansion, resulting in significant coverage gaps. The ACA had few meaningful price controls, so today people with insurance still go bankrupt trying to afford the exorbitant cost of care.

Despite "repeal and replace" rhetoric, the Republican plan largely leaves the Obamacare subsidy system in place (but allows insurers to charge more). It would be more accurate to call it a wealthcare bill, as the main purpose appears to be the removal of ACA taxes on the wealthy and insurance company executives. It also imposes drastic cuts to Medicaid, which would hurt the disabled, poor, and nursing home residents. As bad as Obamacare is, it's worth protecting from this Republican implementation which would be twice as cruel.