Much of the criticism (but not all!) of capitalism boils down to people shooting the messenger. It is a rough world out there and you do need to find some way to compete, but some people would rather hear from people singing about how if you just give them all the power, their philosophy will erase that from the world and you can just go to sleep peacefully and stop worrying. Unfortunately, this is also a lie, or at least that's what the history shows.
Nor does this mean that we are somehow obligated to "maximize" brutality or something stupid. It means that by facing it squarely, we are better able to deal with it, and that's why the capitalistic countries of the world are far better places to be than the places that reject it. It may not be perfect, but by aligning oneself with the true nature of the world you end up producing enough excess wealth to be able to seriously engage in social programs. It's OK to wish it weren't this way... it's not so OK to think that if we just close our eyes and wish hard enough we can make the problem unexist. That leads to actions that leave you vulnerable and exposed. Facing the truth is part of the path to changing it; denial often just makes it far worse.
EDIT: It is a rough world out there and you do need to find some way to compete
That survival depends on competition is a religious tenet, an ideological rationalization.
It is a wonderful thing that humans cooperate enough that we can build enough wealth that some of us, even many of us, can forget this... but the fact that the human strategy is ultimately one of great cooperation doesn't change the fact that the human cooperation lives on a substrate of vicious, no-holds-barred competition, induced by the physics of how this universe works.
Realizing the world is built on competition is not what breeds viciousness... it is what lets us successfully build the secondary layer on top that shields us from it. Those philosophies that try to take a shortcut and declare that the world is not a competitive place have the paradoxical effect of exposing us all the more directly to the raw competition again, because it causes people to build structures that, in their denial of the nature of reality, therefore fail to insulate us against it.
The first step to solving a problem is ever and always clearly identify the problem, not refuse to see the problem.
I'm actually the first to say that A: it's all energy and atoms in the end and B: the universe is awash with both and it's mostly our own stubborness that prevents us from claiming both since we don't "like" nuclear. However, even a Kardeshev Type III civilization will have to contend with the fact that its resources are finite, and as rapidly as its ability to exploit them grows, its desires are likely to grow even faster.
It's not capitalism that causes that, either... a great deal of our desires expanding faster than our resources predates the entire concept, and the problem will likely outlast it as well.