Before you blame climate change on capitalism, please note the coal mines in North Korea and in China.
Nothing could be more equitable than people keeping whatever share of the pie they have earned.
I also truly do not give a fuck about start up founders... but if they aren't well-rewarded then they won't bother. What replaces them? Do you think that instead the government would operate all businesses? Without the possibility of bankruptcy, bad businesses (operating as government agencies) will continue sucking up subsidies. New ones will not be created unless the dictator is convinced that they would be useful to him.
The corruption problem we now have with politicians is indeed bad, but clearly this hasn't become universal throughout our culture. In a communist society, one might pay the store clerk a bit of extra cash to have him hide a bit of meat in order to save it for you. It all becomes totally habitual with all of the ordinary people you interact with every day. It's not just a matter of politicians.
I agree that the situation in the Scandanavian countries is unsustainable. Freeloaders are an increasing problem. The workload (taxes) have reduced the birthrate, and the low birthrate means that fewer workers will be sharing the load of supporting the old, each problem leading to the other problem and thus these countries are in a death spiral.
Why should we risk it? You might say that previous attempts were "not real communism", but that is what we end up with when we try. We've killed 160 million people trying to implement communism, or at least following leaders who tell us they will implement communism. It doesn't seem wise to try again, does it? Why would things go down differently? It's awfully risky to take the gamble, don't you think?
What motivation would there be for start-up founders? If that just isn't needed because the state owns all business, how do we ensure that unproductive business doesn't uselessly stay funded while productive business is never initiated?
If there is no legitimate way to obtain great wealth, don't you think people might turn to methods that are not legitimate, such as the corruption? History shows that communism quickly turns the culture toward corruption, and that this dissipates very slowly once communism is removed.