In a slave economy, slave owners seek technological innovations that make slave labor more productive. But they also place inefficient and artificial limits on innovations that might change the established social order.
Because the rich generally save and invest more of their income than the less wealthy, they are the primary builders of the pool of available capital. Taxing away their incomes means less capital for everyone.
Although many Americans often conflate the two ideologies, conservatism and (classical) liberalism are historically quite distinct. Indeed, conservatism has long been explicitly hostile to both capitalism and classical liberalism.
Reparations advocates wish to tax countless millions of Americans descended from people who only arrived in the US after slavery was outlawed, and thus couldn't have possibly been responsible for slavery.
GDP can be increased through both government spending and printing new money. So, naturally, once lockdowns end we'll see a big rebound in GDP. But that doesn't tell us if the private sector is actually better off.