If God exists, why does He allow evil to exist?
Since this question has been answered countless times, let me just give an answer with a little different angle.
God’s Holy character cannot abide evil in His presence. Every person has sinned (Rom 3.23), so every person is evil (before salvation). That is not arguable.
If God did not “allow evil” (mercy, patience) for a short time, giving us the opportunity to repent and be saved… then His only option would be to go ahead and destroy EVERY person and cast them into hell. And He would be right and just in doing so, because every person has sinned by their own choice.
So in a sense, God in His mercy, allows evil, for now, in order to give us an opportunity to turn to Him and repent.
(There are many other theological issues that have been written about over and over; this is just one particular aspect to consider).
Here are some Bible verses about God’s holiness: