I'm with you. Perpetual economic growth is is undesirable and impossible, so long as we remain an earth-bound species. The laws of thermodynamics guarantee this (of course, we'll be hitting ecological limits long before we reach the physical limits of how much economic activity we can sustain).
Problematically, we live in a society that considers a failure to grow, even for the briefest periods of time, a disaster. We call it a "recession" and we panic and sell our stocks and companies fire people while the media stokes the flames. We run a Ponzi scheme (social security) to support our elderly, which explicitly depends upon an ever-growing economy (and population) to make good on the promises that were made to our parents and grandparents. Economists don't even take the idea of a steady-state economy seriously. We have Keynesian economists vs. classical economists, and more recently behavioral economists, but none of them have the capacity to look beyond their own noses to consider what a truly sustainable economy could look like. The only people sounding the alarm are climatologists, but half of our political class actively works to undermine and discredit them. No worries, though, because most of the population would rather plug their ears, rev their engines, and pretend there isn't a problem.
So what do you do? How do you change the rules to a game that you don't control? Frankly, aside from active advocacy, it's tough to see a more reasonable solution than what MMM proposes: drive less, live in a smaller home, have fewer children, and support sustainable energy. Most importantly, inspire others to do the same. Yeah, 100% of my net worth is tied up in index funds. I suppose it would be more befitting of my philosophy to invest only in businesses whose practices I support, but frankly it has far more of an impact on the bottom line when I buy from businesses I support and refuse to buy from those that I don't. And if my portfolio fails because society has decided to transition to a sustainable economy, I'll consider that a win and gladly go back to working to support myself (spoiler alert: it's not gonna happen).