Then what is purgatory purifying people FROM?
When my youngest brother was around three, he came up with this imaginary monster called a “geen gongee” (I know, even he admits now he had no idea what that meant). When we would ask him what a “geen gongee” was, he would reply, “A gonch”. When we would ask him what a “gonch” was, he would say, “A geen gongee.”. We would ask him where the geen gongee lived and he would say, “In a gonch house.”. That is sometimes what I feel like we go through debating the dyed in the wool religionists here. No real answers can come because they say things they were told yet, without doing any of their own objective research, they swallow it all. So, naturally, all that can come back up is the geen gongee/gonch conundrum - but they don't know why.
Not from sin. It purifies from the defects of the soul caused by sin. For example, one can commit a sin, say, a theft, and then receive absolution of it. So he is free from the sin of theft, but he still has the underlying disposition of greed. He never commits another theft, because of the strength of his will and the divine grace given him through the confession and the Eucharist. But he is still a greedy man. There are no greedy men in heaven. Hence he goes through Purgatory, to cleanse himself from that.
If you can think of someone who you would hesitate calling a living saint, even though he does not seem to have committed any actual sin -- that is a good candidate for purgatory -- at least in your judgment.
BINGO !!!! Stop asking common sense questions..