Just had to weigh in on this.
In my teens I was obsessed with these concepts, now I look back and there are two important lessons I learned.
1. We cannot understand a lot of things that happen in this world, even if we are given a glimmer of understanding here and there, the big picture is so big. We need to trust Hashem that everything He does is for the best.
2. Do what’s right. Hashem gave us clear instructions, we don’t need guessing games. Follow halachah, do what’s right and leave the rest up to Hashem. I believe judging others in the way newbee suggested is reprehensible. (Sorry, newbee.)
It’s against the way we are taught to think: :”al tadin…” etc.
The only way to treat a person as mentioned above is with compassion. Showcasing him as a lesson to learn is against halacha. (Think embarrassing someone, onaas devarim …)
Oh, and I second Haleivi on what he said about this person in this gilgul being a new person. If he did not do any aveiros in this lifetime, he should be viewed as a tzaddik. I think it’s the Ben Ish Chai that says a gilgul means a spark of a previous neshama (a certain aspect of the soul came down again) but the first person and the second are each still their own unique individual.