I suspect there's a difference between backsliding into drugs and alcohol versus backsliding into unbelief. I can struggle with my fleshly sins and still be a believer. The optimum word I used here is "struggle." It's one thing to struggle with sin and a totally different one to embrace sin.
I agree with you. I would like to add a different dimension. Jesus said that he must go back to the Father so that the Holy Spirit would come to convict the world of its sin and the worlds sin is unbelief in him.
Now if a person who having placed his faith in Jesus struggles with a particular sin/character trait like addiction, anger, pornography or gluttony yet hates it and wants rid of it because they want to be like Jesus to be the person God wants them to be then I would say they are saved but also have an element of unbelief.
Not an unbelief that Jesus is the Son of God who died and rose again but an unbelief that Jesus can heal them and set them free. People can have deep rooted learned patterns of behaviour, psychological problems that cause these character traits which they cannot break. Which as I said is not due to an unbelief in Jesus but his promises.
Most people in this situation will lack belief that God so much loves them that he died for them as they are and not when they break these traits. If they go one day without getting angry God loves them but if the next day they get angry then God does not love them. They have a twisted concept of grace and God's love which leads to works based theology/salvation.
They don't embrace sin but neither do they embrace the promises of Jesus and the power of Holy Spirit to help them and release them, set them free. Satan has a foothold and has caused barriers to build up against the grace and love of God which further paralyses them.
Those that are mature in the faith should be able to discerne this. Jesus himself said that the only work God requires is for you to beleive in me. When a person does that we need to remind them of that and remind them that Jesus also said you shall know the truth and the truth will set YOU FREE.
I had to remind someone the other day who was struggling that a man came to Jesus and said I beleive but help me overcome my unbelief. (Mar 9:21-27) Jesus healed the son.
A person can also have a twisted concept of Gods love and grace, this manifests itself as I can do what I don't want and it does not matter, if I sin more then it's covered. We know that Paul addressed this in Romans. So when we come across those people like Paul addressed in Romans we need to teach them that Jesus did not die so you can sin without consequences, then we need to explain what the Gospel is all about and that Jesus does expect a response that wants to be more like him and to die to sin and love God with all our heart and our soul and love our neighbours like God loves us.
If such a person refuses to change then they embrace sin, to me they are not saved and we can as Jesus says "Do not throw pearls to pigs cause they are just gonna trample over them"