Is saying "A curse upon Bani Hashim" or "The cursed lineage" considered disbelief (kufr)?

Cursing Banu Hashim is a grave denouncement, and there are three differing opinions concerning it: one becomes an infidel merely by doing so; or one becomes an infidel if one does not intend to curse the wrongdoers among them; or one does not become an infidel but is to be severely punished.

Cursing is not among the manners of Muslims; for the Prophet, peace and blessings be upon him, was sent as a mercy, not as a curser, and those who curse much will not be witnesses or intercessors on the Day of Judgment. Cursing a tribe is a great fabrication, so what if it is Banu Hashim, whom Allah chose from Quraysh, and from whom He chose our Prophet Muhammad, peace and blessings be upon him? Whoever describes Banu Hashim as a cursed lineage does not know the status of the Prophet's family and must be severely punished, and perhaps even becomes an infidel merely by this statement.