John Adams and George Washington believed a two-party state was a major threat to democracy, and it's pretty easy to see why.
The reality is Democrats and Republicans are about 6 inches apart on every single major issue. Compare the platforms of the "left" and "right" here to other major democracies worldwide, and you'll see.
Things are a little different with the current administration, but even that, the concrete policy and substance issues aren't all that far apart.
- Neither side supports socialized medicine.
- Neither side supports free or cheap college or doing anything about student debt.
- Neither side supports decriminalization or legalization of narcotics.
- Neither side is interested in reducing defense spending.
- Neither side is interested in immigration reform (as evidenced by the Obama administration having, for a long time, controlled both houses and the presidency and changing literally nothing).
- Neither side is interested in reforming the intelligence services or closing GITMO -- remember that?
- Neither side is interested in prison reform or policing reform. Police in America kill 10X as many people per capita as Canadian police kill. The only leader to actually implement any form of prison reform in decades was Donald Trump, credit where due. And that's likely only because he's not really a Democrat or a Republican.
- Both sides persecuted and prosecuted Asange and Snowden.
Really, what are the major points of policy differentiation? A 2% tax hike on the wealthy?