From what I remember, in polite circles it was always known that you should never discuss politics and religion with anyone except your immediate family and close friends.
"The Fall of Public Man" argues that we actually used to be more political and had to "put our cards on the table" so to speak. This would be as opposed to now, where we are very much able to hide our positions if we so please.
I don't know what polite circles would be, but I suppose some sort of aristocracy? Certainly gentile society in 1780s in France were not scared of expressing heavy political discourse in public. Nor were the rich Romans.
Edit: And just to be clear. Rich people may perhaps only speak politics with their closest friends, but they certainly act politically with the use of their capital. Imitating them by shutting up has no point and is detrimental to a democratic society.
The polite society he refers to which originated this standard is the English gentry, with whom American political culture has much more in common than either the Latin aristocracies you mention or the Gallic working class.
In America there is a tension between Jacksonian public man populism of the type you allude to and gentrified politesse of southern planters and northern merchants. In short, you’re both right.
How? If I go to the town square and yell at crowds about how one race is superior to the others, I should expect some repercussions. Why is it different, now, just because it involves computers?
It depends. If the "wrong cause" is one advocating for fewer rights for fellow humans, most reasonable humans feel hard to sympathize with the person complaining about it.
