I always thought man-eating halflings were just an extension of the "normal" halfling fondness for food. "Normal" dwarves love work, so Dark Sun dwarves are bonded to their work to the point where they can become undead if they abandon it unfinished. Elves are a bit flighty, so Dark Sun elves become nomads (with a fair bit of Roma stereotypes latched on, though it's hard to separate general distrust of non-settled people from specifically Roma stereotypes). And regular halflings like eating, so Dark Sun halflings like eating... people.That's all fair, but after giving a fair hearing to these arguments and knowing the topic, I'm still not sure which ethnic group the Dark Sun Athasian would be parodying, and thus who would be the victim and target of the stereotype here. The trope of the "tribal cannibal" has an unpleasant history, when it was used as an accurate description of how certain real world people engaged in cannibalism and with an implicit negative moral connotation (and it was always wrong anyway because real cultures were some forms of cannibalism are socially accepted always have it involved in the context of specific religious or social rituals), but the trope doesn't have to be used like that nor it is used like that in Dark Sun.
Another aspect is that eating people isn't the point of the halflings. The point is that they're xenophobes, and will likely kill anyone entering their territory. And hey, if you're going to kill them anyway, there's no point in letting all that meat go to waste...

