How are we deciding what gets made and for whom? Does democracy get to decide if you deserve a new car? Does a bureaucracy get to decide?
Lets cover an economic concept quickly, given options, people will trend towards rational self interest. If two people agree to a deal voluntarily, they must each believe that trade increases their subjective well being.
In a market system, people can aquire goods and services in proportion to the value they create for others. It isnt decided from way on high, it is the product of a complex social system and the choices we make in it. Since we can assume that people will trend towards their rational self interest, the economy will grow simply as a byproduct of the individuals involved having their needs met.
To have degrowth, I have to question what measures are required to so disrupt the natural order of markets. Now, there are ways, you could use the law to restrict peoples options both legally and economically, but that is dystopian and regressive. Any governing body given the power to decide what goods and services others are entitled to, are violating those individuals human rights to things like free association and autonomy, and are guarenteed to be captured by entrenched interests.
If you just think people are too wasteful and careless, I agree, but I think you need to dig a bit deeper at why people are acting this way. You cant effectively save dollars for the future, and the stock market is a casino; I think people waste because the concept of saving has been turned into a charade. I'll lose it gambling on an auto industry that looks ready for bankruptcy, or lose it when my short position gets blown out by a bailout, and itll be worthless when I need it if its in the bank, so ill buy a new $300 couch and plan to replace it in a couple years.