I am inclined to agree with this at this point in history, but I don't think it is true in general. The Republicans were a conservative party back in the 1850s too, and in part, loyalty to and acceptance of the authority of the church motivated an opposition to slavery, in addition to the obvious moral case made by considering care, fairness, and liberty. (I am also not certain that the Democrats' moral tastes were the same back then; I rather suspect not.) Likewise, the communist revolutions were fundamentally a left-leaning revolution, very very heavy on care and a particular flavor of fairness--and that turned out spectacularly awful.

As Haidt explains, if the moral tastes are evolved, they evolved because at the time they were required for success, and it's hard to envision how our ancestors could have been successful with the "least number of quality lives lived".

I think it's more likely that the problems with conservatism come because we live in a WEIRD society: Westernized, Educated, Industrialized, Rich, and Democratic. WEIRD societies have the capacity to deliver very high quality lives to their members, but at the cost of not aligning all that well with many of our instincts.

In fact, the regular taste receptors give us problems these days: our sugar receptors drive us to eat too many sweets and carbs, leading to tooth decay and diabetes; our salt receptors drive us to eat too much salt, leading to hypertension and kidney failure.

So it would be little wonder if there were problematic sides to the moral tastes too (here, I'm provisionally accepting that they exist, though I don't think the science is settled). I think the right wing in the United States shows an excellent example of those things having gone awry.

But I don't think the tastes are all completely useless at generating a quality society. The January 6th insurrection was a failure of loyalty (to country) even more than it was a demonstration of loyalty (to Trump). The Black Lives Matter protests were a powerful engine of potential change, but the associated riots were in part a failure of acceptance of authority and loyalty to community (in addition to being unfair and harmful).

So I think we ignore the extra tastes at our peril--and blindly accept them at our peril. Conditions today are very different from in the past, with lots of opportunities for improvement and lots of tools to make sure that we're actually improving rather than making things worse (so long as we actually bother to use them, which is rather more rare than I'd hope). Adherence to exploitative authority, loyalty to bigots, and insistence on pure adherence to outdated norms of behavior are all profoundly damaging. But just as a little salt can improve our dishes, a little respect for the authority of our democratic institutions, loyalty to the society we've built even as we seek to improve it, and purity in the face of a pandemic, can make things better for everyone.