Younger and higher educated people are likely to be healthier, eat more consciously, spend more time engaging in sports, have less stress etc. And skew liberal. Lots of potential spurious relationships here.
These are all reasonable points. However, I have read that poor people are more likely to be overweight than wealthy people. The reasons for this are fairly obvious, having to do with being able to afford a better diet, and having more leisure time to exercise. The poor are, contrary to some social conservative myth, notably more likely to support abortion rights than the wealthy.
I'm really not sure how much that counteracts your valid points, other than to note it's not quite black and white.