I fully support The Ink Well's rights as a curator and publisher to have strictly enforced rules about what they will publish. I also agree that the world has enough violence in it.
I do not agree with your implication, though, that violence in literature cannot help build a better world. Some of the most important works of literature in building a better world use graphic scenes (The Grapes of Wrath, A Good Man is Hard to Find, Beloved, Roots, etc).
They are done artistically, and the works would be much worse if censored or left out.
Sometimes it takes building up to a moment of difficult reading that gives the rest of a work the emotional resonance it needs to really have an impact on people.
There are literary works that are extremely violent and that leads us to reflect.
However, I have read texts that describe violence and wallow in violence without leading us to any reflection.
What is the purpose of these texts?
I live in a country where there is violence every day. There are writers who describe the brutality of my country in order to leave a testimony of what happens here. They do not necessarily mutilate or rape in their texts.
Good literature is more effective if you know how to use it.