I would argue that if there's anything true about American Society and the US Government is that we continually trend toward authoritarianism and there is no such slippery slope when it comes to the loss of freedom.

The 13th Amendment and 19th Amendment are both net positive on freedom. Many other counterexamples exist.

The 19th Amendment was signed in 1920.

Perhaps I should have said "since the Red Scare" or "since the War on Drugs"

The civil rights movement came after “the red scare”.

In fact the end of McCarthy came after McCarthy. That particular abomination universally being understood as one the darkest periods is also progress.

I’m also somewhat certain the idea of any net loss of freedom over the last 50 years would be considered a bad joke by anyone not cis/white/hetero/male. Into the 70s, you weren’t allowed to take a job or have a bank account without your husband’s permission.

And if you insist on limiting this to just the freedoms of the all-American white bro: the Boomer generation was still subject to the draft. Spending two years in an Asian rainforest in perpetual danger of dying would seem to be quite worse, liberty-wise, than... whatever you're calling "authoritarianism".

Marijuana legalization, etc. The point is that your claim has thousands of counterexamples and so is fairly nonsensical. If anything, net freedom has been continuously increasing, especially for minority groups.