Because, as noted in Akira's post, the alternative is humanity being made unable to commit negative acts. Everyone incapable of being anything but good and kind to one another. Because the vast majority of human suffering is either inflicted by humans upon other humans, or can be easily mitigated by humans if we were willing to do so.
No child HAS to starve. We have food enough for everyone.
No person HAS to go without shelter. We have space enough for everyone.
Even disease can be conquered, or at least mitigated, if we as a species decided to go for it.
But we have free will. We have a choice. And we make the selfish one every single day.
That's why it's a free will argument.
If there's a god or gods, be they benevolent or otherwise, they do not allow "bad things" to happen. They provided us with the means to better ourselves and allow us to choose whether or not we do.