Let there arise out of you a group of people inviting to all that is good (Islam), enjoining Al-Ma'ruf (i.e. Islamic Monotheism and all that Islam orders one to do) and forbidding Al-Munkar (polytheism and disbelief and all that Islam has forbidden). And it is they who are the successful.
3:104
What do you have to say?
No one here has argued that one cannot advise someone about haram and halal.
You have made a strawman.
What the user @GalmudugW said was that we should not judge or backbite sinners.
That is completely different to saying “no one should ever advise people on haram unless they’ve never sinned.”
That’s an impossible argument.