I firmly believe that economic pressure is more of the main reason for the decline rather than education or healthcare. So you're right about the quality of life thingy. I'm fine right now to start a family but the resources that were supposed to be mine will be re-allocated to others needs. Unless you are talking about the conservative people or religious freaks who do not accept or have sex education in developing countries though.
Every country in the world is at stage 3-4 of the demographic transition. Most are already stabilized aside from Africa. It is presumed that the world population would stabilize around 10 billion~ so I don't worry a single bit about the earth as a whole getting overpopulated. What I'm worried about is how some countries' social security is designed like a Ponzi Scheme; the old generation reaps the retirement income benefits, while the younger generation pays for it. But with declining birth rates and increasing retiree rates... this burden falls upon the younger generation. Hence, they have to pay more.
Deeping deeper here. We're talking about the population as "global", but the pop density per country vary. That's why we are currently having a crisis caused by "overpopulation" to some countries.
Water shortages: Becoming a problem in some countries (not you Canada)... say in Baja Cal Mexico. But not so deep that people would die from dehydration. We don't want a repeat of the Cape Town water crisis lol.
Increase water prices to force people to conserve. I personally think this is the only way for some. Salination is inefficient and expensive. Anything that could improve distribution like piping is also cool. In any case. We are using more water than nature to recycle your pee (fuck treatment plants! its always nature! and dolphins)
Meat shortages: Also a thing. With other nations developing (say China). They're adapting to another diet (Western meat yummy yummy) thus increasing demands for meat that it's becoming unsustainable. Good video here.
https://www.youtube.com/watch?v=FqGI3iMX_co
Improve and accept plant-based (still yuck) meat and/or cell-based (more hopeful in these) lab-grown meat. Or reduce meat intake overall. This solution also helps with our problems with CO2 emissions (those damn farts) and water crisis (animal/dairy industry uses a lot).
Antibiotics Resistances: Caused by overpopulation too. Used extensively in animal agriculture.
Reduce this and that and so on... Cause and effect.
Limited resources: Coal (Magnolia says we have a lot of it..) Oil (Oh the arabs says this shit will ran out after a few decades. But the Ruskis in the Urals may veto this statement thanks to climate change) Nat Gas (Gonna take long to diminish.. China currently building pipelines to Iran yippie).
Solution: Elon Musk and/or Ernest Rutherford
IoT: Yeah just gonna add this. In case yall don't know. We ran out of ipv4 addresses long ago. But we're transitioning shits with ipv6 yippie. Overpopulation plays a role but this is actually about the huge increase in average device per household.
And all of these problems are caused by overpopulation yeppp. There are long term problems. But humanity is going to fix this, and we'll survive
Oh yeah.. Not being a know it all, that's just my personal view and I'm sure there's a flaw on my statements.