I enjoy gourmet cuisine as often as the bathroom scale will allow me to, but I have no problem with the proliferation of restaurant chains which often replace so-called "mom and pop" places. They seem to provide a reliable, convenient, consistent, and typically affordable product to the general public, which appears to prefer going to such places rather than the higher-priced mom and pop. While the inefficient "mom and pop" places may be disappearing, there is fierce competition between the chains for customers, so they are constantly tryng to improve their products and service per customer dollar spent.
When I'm on the road somewhere in the boonies and I want a quick meal and break, I'd rather head into one of the known brands than risk stopping at the unknown taqueria and landing up with slow service, food poisoning, no air conditioning, filthy toilet, etc. The local "color" in such places simply doesn't make up for the "dining" experience I have there.

As for obesity, well, that's another complicated story I have a professional interest in. Our society has gotten so affluent and the overall price of food has come down so much that even poor people can now afford to overeat and become obese, especially when coupled with less overall physical activity (more TV, more FT surfing instead of wood chopping, etc.). Though fast food restaurants provide an inexpensive product with a lot of calories/$ spent, it is ultimately the individual who decides to keep overeating even though he is obese. Eating a hamburger from McDonald's isn't going to make you any more obese than eating a hamburger from a local mom and pop restaurant or a hamburger your mama makes you at home. The problem is when you continue to eat more hamburgers than your body can burn off, and the challenge is to figure out how to get people to stop stuffing themselves, now that almost everyone in the U.S. can afford to do so.