system
Given the following post, respond as if you're commenting on Reddit:
human
[MCU] Who/what decided Red Skull's penance? And why? And why only him?

The only clue we have is that the Space Stone cast him out. Okay, makes sense that one stone would connect to another one. But why? Is it because he abused them for power? Lots of MCU villains have done that and been fine. It's not because he directly touched it, because he didn't. There was a cube of something surrounding it. Besides, Jane Foster *did* directly touch the Reality Stone and all it did was try to kill her. It's not because he wasn't strong enough, either - see Jane Foster. Is it because he tried using it for raw power when its purpose is to move through space? Did it maybe just send him through space because that's what it does, and the Soul Stone did the work? Did anybody else in all of history get judged like this? And how did Red Skull know any of this, anyway?
gpt
The Space Stone itself is said to possess some form of sentience, unique among the Stones. People who study it closely will refer to it as "she" and keep imaging the Stone purposefully trying to show people stuff.  When the power was turned off on the device uses to harness its energy. the Space Stone turned it back on by itself. 

So, the Space Stone decided Red Skull was abusing it, and took matters into its own hands to punish him.