What else did you think all the Fallen Empires in Stellaris did ? ;-)

Some say they’re still in there to this day.

Also with people having fewer ties to the rest of humanity, there will probably be some weird effects on morality

Some will, and they will outcompete.

human advancement is a function of population, instead of focusing on population decline to solve our resource problems we should focus on efficiency and technology. i am not rooting to revert to the dark ages i really struggle with this ideology of reduction that seems extremely popular. we really take for granted the fragility of human existence we exist in a pico second of reality and could and most likely will be snuffed out eventually, having our own species rooting for this outcome seems suicidal.

so pretty much anyone who isn't amish?

In the future you won't be able to tell.