This isn't going to be terribly popular but I'm a conservative (not a Republican but a conservative) so I'd like to discuss what you said.

The 1960s saw progressive tax rates up to the 90% range on top earners

That ended in the 1963. Most of 1960s the rate dropped from 90% to 70%. In addition, when the 90% rate began, it was really only applicable to a handful of people.

However, that's marginal tax rate as opposed to effective tax rate. The effective tax rate is mathematically lower than the marginal tax rate so even the 70% rate didn't mean that's what was paid.

But that simply does not matter for one major reason: the very wealthy simply do not pay much income tax because they don't earn most of their income that way. Most pay long-term capital gains tax which is capped at about 20%.

We saw a civil rights movements and African Americans improving their status.

I admit that it's baffling to me why conservatives would be against this unless they're simply racist. As a conservative, having more highly educated people with high paying jobs would not only increase the US GDP and tax revenue (i.e. more money = lower deficit and maybe a surplus without cutting critical programs) but also increases our status as a country.

The feminist movement started, as did the sexual revolution.

That movement started way before 1960s. Women's suffrage already had conventions at the time of the US Civil War with most of the states supporting it - and the 19th Amendment - in 1920.

Thanks to government investment we became the absolute world leader in science and technology.

To be fair, it did help that the rest of the industrialized world was destroyed after WWII and we got many of the top Nazi scientists like Werner von Braum who pretty much built our space program.

Convervatism is a commitment to traditional values. Those values are upset by liberalism that wants to push the envelope. Some of these liberal values are good and become conservative values by definition. Think of it as a tree: conservatism is the trunk and liberalism is the new growth. Both are needed and the new growth becomes the hardened trunk over time.

What you're talking about - racism, sexism, desire for ignorant masses - isn't conservatism, it's modern Republicanism.

At least that's my unpopular opinion. Unpopular because many liberals would dismiss what I have to say simply because I don't consider myself one and too many conservatives have become Republicans.