I've heard of suffering for one's sins but what a group of Catholics is doing in South America is just plain wrong. I recently watched footage of a group of Catholics who were voluntarily nailed to crosses to atone for their sins and to show their dedication to Jesus.
They are wrong. God doesn't want us to punish ourselves and to physically torment ourselves in the name of worshiping Him.
Long ago, self-flagellating was viewed as a way to discipline the body and the mind, atone for sins, etc. This practice is no longer condoned by the Church. One can make up for sins through prayer, true reconciliation, penance and good works. If you are truly sorry, God will forgive you your sins.
I can't help but wonder how seeing His children hurting themselves affects God. Imagine this, you have a young child who is fresh, or who even steals something or some other act you disapprove of. Now, after the tears and the punishment (no TV maybe?) your child takes it a step farther. You think the matter is resolved but he decides to show you just how sorry he is. You discover him in his room repeatedly bashing himself on the head with a bat. How would that affect you? Would you say - oh now I know he's really sorry? Probably not. As a parent you knew he was really sorry before all this. Instead, you are incredulous and incredibly alarmed. Your first reaction is to stop the child. You never want the child to hurt himself.
Now, if we look to God as our heavenly Father, how could we possibly think that hurting ourselves would be pleasing to Him?