condeming a brother to hell
I agree condemning those that have Christ in them to hell is indeed wrong. But telling people that do not have Christ in them if they rely on their own good works to save them - these will not like where they end up and that is right and loving.
I firmly believe Christians that have Christ in them can be all messed up in their thinking because of false teachings and thus think all that good works save them - are in fact stills saved.
They are just trying to live by their own self-effort of the flesh and do not yet have a revelation of the gospel of the grace of God in Christ's finished work on the cross and resurrection.
Our Lord will be faithful to them to reveal Himself and all that He has already done for them because of His great love and grace towards them.