Well the first basic answer is that it's clearly destroying the entire planet with no logical manner to stop. Global warming is getting worse and worse with no ending in sight. Air and water pollution are getting worse with no ending in sight (the fact that western nations have outsourced much of their pollution production to 3rd-world nations isn't an improvement). The world's fisheries are nearly all collapsing, with no plans to stop the collapse. The world's rainforests are all being cut down or burnt down and there's no way to stop it. Soil quality is degrading everywhere. Carcinogens are more prevalent everywhere. The amount of trash produced is increasing dramatically. We could go on an on. The desire to turn every product of the Earth into a commodity means that someone who wants profit will eventually take everything.Average people now have the power to live like the kings of old. I fail to see the problem. At one point, running water was a luxury. People are moee productive than ever before. What once took a factory to produce, can now be produced by a garage. Diseases that once threatened entire nations have been eradicaded. Capitalism isn't perfect, and the problems are more due to its inherent amorality (even Adam Smith acknowledged that capitalism needed outside moral guidance, in his mind religion), but it's created more prosperity for more people than any other system.
Then look at mental health. If life is so good, why are depression rates going up? Why is anxiety going up? Why are more and more people getting medicated (or self-medicated) in order to deal with the basic functions of life? You walk into the conversation assuming this thing "prosperity" as a positive good. There may be certain correlates with materialism that are good, but materialism itself seems to have created a lot of lives that are deeply unsatisfied with their situation. And this isn't just a 1st-world problem - in 3rd world nations there are now over one billion people living in slums. By capitalistic measures a slum-dweller has an income MUCH higher than a village-dweller. But is their life better? Have you ever asked them? Is living 6 people to a room in a polluted, smokey, concrete-filled, disease-filled slum with constant fighting due to the extreme overcrowding a better life simply because you now have a higher income (much of which is spent on things like rent and groceries that you used to produce yourself), plastic products, tv shows and a mobile phone?
Even if you believe that it was capitalism that caused the actual good improvements about modernity (and not scientific and political developments that had little to nothing to do with capitalism), you have to admit that something which was good at one stage of economic development is obviously not the right approach now. Capitalism guarantees that the planet's resources will be destroyed and everything will be commodified and both environmental and human well-being have no place in the equation.