The Left believes that private sector growth (and GDP growth in general) is a given, a baseline if you will. They've convinced themselves that the Keynesian multiplier is greater than 1.0, in other words removing capital from the private sector in the form of taxes and spending that on various forms of government-sponsored consumption results in a higher overall GDP than leaving the capital in the private sector.
The Right believes that this is nonsense on stilts: that the multiplier is certainly less than 1.0, and may even be negative for many types of government spending; that the drag of increased government headcount leads to make work jobs which result in the creation of regulations that depress private sector GDP growth; that spending programs are not designed by Philosopher Kings, rationally analyzing which programs would produce the greatest multiplier effect, but rather are determined by political lobbying from powerful interest groups.
There's no bridging this divide. This is a fundamental disagreement on starting principles.
Perhaps the greatest evidence that the Left is not smarter and more nuanced than everyone else is that they simply refuse to debate this disagreement. If their argument were as powerful as they claim, they'd be happy to do this. Instead, they point out that the debate is long over, and even Nixon said that "we're all Keynesians now".
Let me emphasize that: the Left is using Richard Nixon as an example of a Philosopher King. Seems legit ...