> they suddenly weren't. Eg: Monarchies, slavery, beasts of burden, and diseases such as smallpox.

Except that every one of those things still exists! Smallpox doesn't exist, but other diseases such as syphilis do.

So that actually demonstrates exactly the opposite of the point you were trying to make.

Monarchies is an especially bad example because they still exist precisely because people are unwilling to stop a tradition that has gone on that long.

> Monarchies is an especially bad example because they still exist precisely because people are unwilling to stop a tradition that has gone on that long.

I'm not sure that's the reason; perhaps the largely-symbolic monarchies of Europe, but the substantive monarchies in the world are actually mostly quite newly established.

Slavery does exist but in 1st world countries people do look at it with bewilderment even though it is still around in some places.