I don't think the argument is erroneous. From talking to people who grew up before the Web became mainstream, they said that since your social circle was typic

I don't think the argument is erroneous. From talking to people who grew up before the Web became mainstream, they said that since your social circle was typically neighbors and colleagues, there was much more incentive to be civil because you were going to see those same people almost every day. Once the Web became popular with the mainstream, people started to form ideological bubbles because now you could pick your social circle, causing people to grow accustomed to everyone agreeing with them. Once in their echo chamber, they don't need to defend any of their beliefs, causing them to lose the ability to have civil disagreements with people they disagree with, and they don't need to, because they can just stay in their bubble and surround themselves with thousands of people who all think the same thing.