Growth isn’t a problem when it’s sustainable. However, there are natural limits to how far and how fast technological development and resource extraction will allow us to grow the economy.
Additionally, competition within capitalism forces the wealthy to seek out any and all means of growth. If they do not they actually risk all of their wealth becoming devalued. This drives innovation but it also is the driver of imperialism, exploitation, environmental degradation, all of which grow the economy.
When growth because less attainable due to various natural constrains, the wealthy start to cannibalize the systems that keep society stable. Again, they can’t help themselves. If they don’t their class position is threatened as some other capital owner beats them to the limited profits that come from privatization and austerity.
This usually results in mass unrest across all the various classes in society. That includes some of the middle classes who also rely on exploitation to maintain their standard of living. In response to threat of social unrest, the wealthy usually align themselves with right wing authoritarians that claim to be able to bring order to the chaos and renew growth through imperial expansion. This kind of politics is often supported by some of the downwardly mobile middle classes. That’s how we get fascism.
I doubt the person you’re replying to would disagree that the advent of capitalism is in fact what brought liberal democracy into existence. The point though is that such progress is unsustainable under a capitalist system and that it will result in various crises, war, and fascism. Therefore we do need to find a way to move past capitalism if we want even the possibility of creating a better world.