Good piece. I’d like to add a little to what you’re saying. While you can’t really say for certain what a historical figure would think if they time-travelled to another era, I think there’s a reasonable case to be made that Adam Smith and Thomas Paine might be something like Marxists if they lived in the 19th or 20th century rather than merely social democrats.
I say that because, as you pointed out, both had a fierce egalitarian strand in their thinking, but neither had witnessed capitalism beyond its most embryonic form. If you apply the Marxist conception of history, ideas are constrained by the material conditions that give rise to them. Smith and Paine’s ideas were only as radical and advanced as the times would allow.
Marx was rooted in liberal thinkers like Ricardo as well as Hegelian philosophy. The advancement of political and economic thought in that direction was only made possible by observing the advent of the Industrial Revolution.
Smith believed that free market capitalism would bring forth “universal opulence,” and it would be interesting to see how he would react to having that theory tested in practice during the Gilded Age. Take that one step—and one century—further and what would he say about the failure of even the welfare state and reasonable regulation to bring about that result?
The same goes with Paine. He had rather radical politics, but I think he was held back by the limitations of liberalism. In Agrarian Justice, you can see something akin to Proudhon’s “property is theft” formulation, but it’s framed in liberal terms, i.e. that the earth is common property of all mankind, but private property can be created so long as the people are compensated fairly for the loss of their natural inheritance.
Anyways, not trying to be self-promoting, but I wrote something very similar to this and I sincerely think you might enjoy it.