Possibly, although it hasn’t stopped people from doing it in the past.

But many people don’t want to have everything completely public

This isn’t true at all. Most people do not care about privacy; those that do are an extreme minority. You (presumably) and I are part of that minority yet even we still comment here, in a public space. The issue with forums has never been about privacy because most are content with pseudonymity. It is a big mistake to think we need to cater to the extreme minority in the privacy space when tackling big issues that involve a majority who do not care.

Discord is far worse in this context, though. Much of reddit is still publicly visible and is still indexed by some search engines, even if it could be better. Discussions from years ago are still visible and provide useful information to many (this is part of the reason “search term + reddit” became such a popular query template). When communities move to Discord, many of their conversations become completely private to anyone who isn’t a member. The conversations move quickly and there is no easy way for people to reference past information. I get that people on Lemmy hate reddit and it’s popular to circlejerk about it, but forums being replaced by things like Discord and Telegram that aren’t equivalents at all has been much more damaging.