I definitely understand your reasonings for that. And I do agree having it default on does help raise awareness of communities.

My main reason that I’m against a default on is I’m always strongly against any type of action that does something on the behalf of someone else without it properly being relayed.

if the person who made the community wanted to advertise their community, they could reach out and send a message on their own, or they could turn it on, but having it default on creates cases like this, Where they weren’t even aware that it was making a group, it seems, until people started messaging them complaining about the amount of spam.