The reason why conservatives of the past seem to be more reasonable is because there’s much more evidence (and easy ways to cite it) to refute their seemingly well-reasoned arguments.

In the past a conservative might say something like, “taxes on corporations are pointless; they’re just going to be passed on to consumers” and they could make a well-reasoned argument from simplistic economic principles.

These days when someone hears that argument they can just look online and find a zillion well-researched and cited articles pointing out how it’s a flawed position based on bad assumptions. Just looking at how changes in the tax code over time (massive reductions in corporate tax rates) have impacted the economy and the price of goods. Spoiler: Reducing taxes on corporations has two effects: It reduces tax revenues (obviously) and makes the rich (owners) richer. Changes in the tax code that increased taxes on corporations also had no impact on prices. In short, the entire idea falls flat on its face even though it seems like it would make sense.

They’re the same conservatives they’ve always been; refusing to change their beliefs despite the evidence. It’s also that we now know more about their beliefs and the more we know the more extreme they seem.

Conservatism has become a political package: By “voting conservative” (making it a part of their Identity) a person is signing on to conservatism as a whole. They may not believe everything their peers do (e.g. racism, xenophobia, sexism, violence, etc) but these things they do not agree with are not game changers. They may not believe that whites are a superior race but they’re OK with those people being on their team.