There was 1.5B when my great-grandparents were born (1898), 3.7B for me (1971). Now there are 8.1B souls, better off economically and consuming to match.
Don't tell me we have enough food, "if it wasn't for evil peoples!". Don't care, we don't have enough water. We're draining aquifers that took 1,000s of years to fill, major cities are basically out of water all over the globe. And that was before AI!
Immigrant hate? Overpopulation. As a kid, most folks looked like you. By middle age, the world is clearly shittier, but the economy was on an upward trajectory for great-grandad, grandad and dad, but not for you. You look around today. Suddenly there are shitloads of poor people who don't look like you! See how that works? (I don't think the haters understand this.)
Global warming? Did I mention people are far better off and wanting their share? Global poverty rates dropped through the floor. The newly "rich" want to enjoy the life the rest of us had. Can't blame 'em. Look at China, still building coal plants to get "caught up". Remember the crazy smog in their major cities? LA was like that when I was a kid.
Hell, even the billionaires wouldn't be so rich and have so much influence if there were half the people to get rich off and influence. Orgs like FB and AWS could not exist as they do now with half the customers, scale wouldn't be there. If I could get one penny off every human, once a year, I'd be making $81,000.
Best part? Depopulation and deflation are economic disasters. Don't know of a time in history where we successfully navigated depopulation in the short to midterm.
EDIT: Forgot to add! We've lost 74% of the animals on Earth since I was born. That's on human activity, and lately, global warming. Our ecosystems are crashing, and unrecoverable in some cases. As one example: There are too many humans who don't want bugs around. If you're 40-50+, you knew a very different world. Hell, if you're 30, I can show you ways the local ecosystem has crashed out, ways you'll remember. "Oh shit! I forgot it was like that!"
Guess I'm wrong. We just need to allocate food, water and wealth fairly (which has rarely if ever happened). Stop pollution in the form of CO2, plastics, herbicides, pesticides etc. All while elevating the way of life for 8B, soon to be 9B, humans. Oh, and every tribe, counter to our entire history and evolution, should suddenly love one another. And somehow, we magically stomp out the wealthy. Super simple stuff! Easier than saying, "Maybe there's too many of us?"
We have 100s of millions living in fucking deserts. Please do tell how we allocate resources?
There are 10,000,000 souls in Tehran, out of water. But if they were just smarter we could support them! The Colorado River is damned near about to stop flowing, as is the Red River. Mexico City is the largest city in North America, semi-arid, out of water.
And here I'm only touching on water issues. How about the rest?
Are you joking? There are hundreds of different ways to get water to them. If you move any physical resources into a place, chances are high you can move water in the same way.
There’s also just building pipelines and extra desalination plants along the coasts or some more exotic methods of water extraction from the air or earth depending on how you want to do things.
Point is that we have the technology to produce as much fresh water as we could probably ever have a desire for. Fresh water is an extensible resource. And as long as we have vehicles, we can get that water to the people who need it (though pipelines would be more efficient).
So why does it seem like water is scarce if it isn’t? Because it requires infrastructure to produce, and—while building that infrastructure is very possible and not difficult at all for a developed country—few countries would pay to save the lives of the less fortunate unless it benefited them economically.
In other words, the scarcity you mention only exists due to the greed and selfishness of those with economic resources. Overpopulation isn’t the issue, economic systems that value money/revenue over the lives of others (capitalism) are the issue.
Edit: Also, the rivers running dry is mostly an issue with wasted water and allocation of that water (as the commenter above mentioned). Both of which would be drastically decreased if profit wasn't controlling their regulation more than preservation or societal benefit.