When I was a child, parents would inform other parents when a child had chickenpox; so they could have a sleepover. That was normal practice in the portion of the USA I grew up in. As a result, nearly everyone my age has natural immunity to chickenpox.
I share that anecdote to point out that the idea of an "infection party" is a really old idea that was practiced at scale. It's not unreasonable to assume people will treat this the same way based on that type of past behavior. Whether it's "dumb" or not remains to be seen.
Edit: I wanted to add for younger persons a blurb about WHY you want to get chickenpox as a kid. Children experience mild symptoms from chickenpox - it's a non-event other than missing some school and having a few sores. Adult cases of chicken pox however are fatal by a large majority.