You talk of imagination but you haven't even described your solution or why it would be better than the well studied economics concepts of free markets with carbon taxes.
At the same time I'm not a scholar, historian, economist, politician, or powerful military leader. My capacity to conceive of another future, or author it, is constrained. My ability to condemn evil where I find it is not, however.
It's like a diabetic stopping their insulin in the hopes something better will come along.
They said we must replace capitalism because of the horrors it perpetrates.
That is a very strong statement.
But I guess they could be saying "we are morally compelled to replace capitalism with a system that may or not work exist that may or may not solve the problems we have attributed to capitalism without showing that any other workable system fixes these problems, only that they happen to exist under our current system."
Which doesn't strike me as the most useful criticism of capitalism.
The person you're replying to has already expressed doubt about whether it's a simple capitalism/communism dichotomy. Responding to a communist straw man of your own creation isn't helpful.