He refused Christian asceticism, the renunciation of life, that pushed the believer to seek pain to imitate the passion of Christ, to postpone his life, to be alive now-dead in the hope of reward later.
The alliance between the Noble and the Church has never been as powerful in the period where Montaigne wrote Of Cannibals. The Noble were ensuring the legitimacy of the Church (and vice versa) for mutual benefit on the backs of the people. To ensure the sustainability of such a system, the Church was trying to fight against all forms of heresy, which would amount to challenge his authority.
Recently, the "new world" was (re) discovered by Christopher Columbus (1492). The France in the EU, discovers with amazement that God created other creatures "in human form." Separated from a known world by the ocean, these creatures could clearly not descend from Adam and Eve (we do not yet know that humanity had a common root in Africa and that the Indians were far distant descendants of Adam and Eve.) Had God so created two kinds of men? The French or European human was no longer the center of the world, the only creation of the Almighty? The French had long debate on this question: could we consider the new world of creatures like men? But these "savages" who practiced cannibalism and human sacrifice, could, for others, be classified as animals, without souls, which took away the Spanish abuses against all sinful dimension and legitimized slavery