It's not a slur except for some Liberals who appear to have invented it.
Was "macaca" ever used as a term for anything, or did it just pop out of Allen's brain as some random neuron fired? In all my thirty years living in the south, I've never even heard the term used at all.
The liberals LOVE equating darker skinned people with "primates" and then accusing conservatives of doing the same. Had Allen simply said, "Welcome to America, young man..." would that have been found racist as well?