Apart for a transcendent God establishing objective moral standards of right and wrong what could ever make suffering (or anything else for that matter) "unjust"?
People with weak uncertain or challenged faith struggle with the concept that “God” is unjust impotent or uncaring ... or worse... and took their child or simply let evil occur and let them die. This concept reassures atheists who do not want to believe there is such a God, or if there is- to respect or submit to Him.
Over 10 years of networking with grieving parents, I believe that people who have faith or who can find it, come to the idea that God did not “take” their child, but received them at the moment of death, and that each of us no matter what age has a personal connection God and with His presence at the separation of spirit from body at end of life, it's not an impersonal process that is in the control of a 3rd party, even a loving parent, and as a result none of us is ever really alone and will all follow the same path, when it is our time.
I saw an interview with this doctor on FOX Business and look forward to getting his book
I was going to say that. There is no concept of “justice” beyond an individual’s opinion, unless there is an ultimate Judge Who is above us all.