The fact is that this racist caricature insults not only your black readers but also any reader with a social conscience. This kind of negative stereotype has a harmful effect on the perception of black people by other groups as well as the self-esteem of the members of that group.
You say that you did not intend to reject any particular group, but in agreeing to publish this kind of insulting caricature of the intellectual ability of a minority, all you do is reinforce the negative stereotypes that we fight against every day. Every day, we live with the consequences of these clichés that, as they become commonplace, end up being accepted as truth.
I cannot agree with your statement that your "new cartoonist started off with a bang that had the merit of sustaining a discussion where not everything is black and white". On the contrary, he has begun with a disastrous and shameful flop in a failed attempt at a cheap laugh. I think you should take the advice of Madame Wilheim of the Greater Châteauguay Association for Minority Rights, and apologize to your readers.
Canadian Race Relations Foundation