Why would an all-good and all-powerful God allow the existence of evil?
The Biblical Christian answer to the PoE is simple: “All things work together for good for those who love the Lord and are called according to His purpose.” Rom 8:28
Simply, what we perceive as evil is ultimately part of a good purpose.
The good purpose is that God (particularly Jesus Christ) is glorified and shares that glory with His people.
We know the reason. We know the objective. You may not agree with or accept it, but we have the answer to the PoE. For the Biblical Christian, it’s not a problem at all.
The foundation for my rationality is rock solid based on my authoritative source of truth. The atheist has much more of a “problem” in that they have no objective moral standard from which to judge what is “evil” or “good”. The torture of a 3 year old holds as much moral and rational weight as buying them an ice cream. It is a precarious basis for morality - rationally more akin to psychopathy than altruism.
Thank God that the foundations of modern social morality is built upon a Judeo-Christian framework and not atheistic rationalism.