I pondered raising this issue in my above comment but decided not to since the comment was already long enough but the issue has been raised nonetheless.
I agree that "the planet can't support X" is code for "I don't want to change my lifestyle" or, by extension, "I want my children to have the same lifestyle".
Lots of animals return to the point where they were born to breed. Some cross vast distances. The human version of this is a mix of normalcy and nostalgia.
By normalcy I mean however the world was when we were in our formative years we view as "normal". I really wonder what life was like 500 or 1000 years ago when politics may well have changed but largely there were few if any substantial everyday technological and societal differences from one generation to the next.
The problem with this is that ew can easily start seeing everything through this lens such that things that diverge from our view of normal are (more likely) "bad" and those that don't are (more likely) "good". This I feel is a big part of conservativism/traditionalism.
The nostalgia is obvious. The time when we were young is often romanticized, even fetishized.
So as to maintaining lifestyle, let me put it this way: assume you're fo middle or upper class in the US. Could everyone in the world live as you do now? No. So by some measures we're already living beyond our (collective) means. And as hard as you may have worked, as smart as you are the biggest difference between you and a resident of some far less well off country is just plain old dumb luck that you were (probably?) born "here" (wherever here is).
Granted some people from more disadvantaged backgrounds do better their lot in life but the odds are stacked against them in a way that just isn't true for someone born in the US, Canada, Australia, Japan, Western Europe and a handful of other places.
Fun fact: the population density of Tennessee is 160/mi2. The land area of the US is 3.8m mi2. If you populated the entire US at the same density as TN you'd fit 6 billion people there.
Would you consider TN overly dense?
You may not have ever been there but it doesn't matter. No one is piled on top of each other (like, say, Hong Kong at ~7000/mi2). People live on large lots in big houses and there's still wilderness.
We only live on a tiny fraction of available land. The vast majority of it is farmland but if farmland can produce 10 times as much per unit area then we need an awful lot less of it to support a much bigger population.
Unfortunately preserving one's way of life is so often just code for NIMBYism, excluding certain groups (eg segregation in the US) and maintaining the status quo just because you were lucky enough to be born in the right place.