Is it a sin to inform a Christian in a harsh manner that he is an infidel and to demand his departure from the forum, taking into account that there are specialists to refute their misconceptions?

Whoever was not upon the religion of Islam after the Prophet, peace and blessings be upon him, is an disbeliever in Allah, and his destiny is the Hellfire. It is forbidden for Muslims to show affection, love, or loyalty to disbelievers. It is permissible to interact kindly with peaceful disbelievers to encourage them to embrace Islam. Women are forbidden from engaging in private conversations with non-mahram men in chat rooms. Warning is given against non-Islamic forums that promote music, indecency, and lewd films.