Please do not trump up ikhtilaaf when there is no ikhtilaaf on this issue. There is clear nass on this issue. The Fuqaha are all agreed that it is haraam for a Muslim to carry out this act. You should be very careful in giving non existent rukhsa and placing a Mumin's imaan at risk. May Allah save us all from this type of misguided thinking. "And never (O Muhammad صلى الله عليه وسلم) pray (funeral prayer) for any of them (hypocrites) who dies, nor stand at his grave. Certainly they disbelieved in Allaah and His Messenger, and died while they were Faasiqoon (rebellious, — disobedient to Allaah and His Messenger صلى الله عليه وسلم)” [al-Tawbah 9:84]. "Imam Maalik (may Allah have mercy on him) said: “The Muslim should not wash his father if his father died as a disbeliever, or attend his funeral, or go down into his grave, unless he fears that he may be neglected, in which case he may bury him." End quote from al-Mudawwanah, 1/261 Brother, if you want to quietly advise the brother then contact some scholars who can provide you with a detailed article stating the ijmaa of this ummah regarding the impermissibility and quietly post it to the brother. This will keep you anonymous and lessen the risk of an altercation. Also make dua that Allah guide the brother and us.