Food has become a statement of moral worth for at least some people. For them, there are morally righteous ways to eat, and other options are sinful. (Swap food for sex if this distinction is a bugbear to wrap your head around.)
If you believe that fast food is essentially sinful but also that poor people are essentially good, then there must be a reason why poor people can't eat like righteous people like yourself eat. Hence things like the economic argument.
If you believe that fast food is essentially sinful but also that poor people are essentially good, then there must be a reason why poor people can't eat like righteous people like yourself eat. Hence things like the economic argument.