Let me start with a couple of facts about myself:
1) I am a Christian. I believe in the Bible, I believe that God is supreme in all matters, and that Jesus Christ died for my sins.
2)As a Jehovah's Witnesses I was never disfellowshipped, or even called before a judicial committee.
I'm saying this so that I don't have to listen to the likes of God Rules telling me I'm unrepentant.
Disfellowshipping as practiced by Jehovah's Witness is unscriptural and mean. Once you become a witness asking the kind of questions you are asking here will get you disfellowshipped. All your new friends will have to stop talking to you.
Yes, you only have to demonstrate repentance to God, but if you don't go talk to the elders that in itself you show that you are not repentant. You will also be required to report any wrongdoing you find out about to the elders.
A number of years ago, while in a state of clinical depression following the death of her father, my wife's aunt fell into sin. What she needed was counseling, medication and support. What she got was disfellowshipped.
Yes, the elders have a duty to keep the congregation clean. In my church this is handled by helping those that fall into sin see that they need to make changes. This is brought about by prayer, study and counseling. I've known of people that have spent YEARS in our counseling programs working on overcoming problems. And I'm not talking about "small" issues. There are groups for those overcoming drug and alcohol and even sex addictions (for example). At the Kingdom hall these people would be disfellowshipped.