I always felt that film was lazy in how it presents its premise.
Maybe there's naunces I'm missing because I'm not American, but it made me feel a bit gross in the same way a lot of pop culture around 'chavs' in the UK made me feel a bit gross. I don't think always refraining from punching down is a good rule in comedy, but I struggle to find much comedy in things which are nothing but punching down.
Idiocracy is more like a work of Baudrillardian philosophy though, it isn’t punching down, it’s extrapolating upwards.