If you max out your ROTH IRA every year until retirement that is possible (for the US). Yes, I believe one can easily save and invest in index funds. Based on compound interest with a return rate of 3-7% one could expect 450,000-1.05 mil after 35 years of working. That’s 583$ post tax dollars a month.
Post kids it’s been more difficult but I even picked up an extra job to make sure I can max out my retirement investments.
For everyone? Absolutely not. It is obtainable though. Even half of that per month would result in similarly good returns. The problem is investment education. Reminds me of my local communist reading group who to my surprise didn’t know anything about investing even though capital is like their whole thing.
I do make maximum contributions, but I also have two kids with college funds and a mortgage that I'm paying down. We're comfortable, and I consider myself extremely fortunate for the life I've built for myself.
Unfortunately, it took me a while to pay off college debts, and then the 2008 crash wiped out a lot of our savings. I don't expect to ever have enough saved to actually retire.
For most of us reading this it is an obtainable retirement income. On the world stage if you can read this you are probably rich. A little bit of savings can get you 3k inflation adjusted once you reach "old age".
That would be achievable in the US as well - 140k US saved and living a "simple life". Those some people who try it go back to work in a few years because it turns out they value a more complex life. YMMV.