In general, if these programs are offered, and you agree with the mission statement, but you are not in need of them (e.g., you're well off enough/not food insecure) --- use them anyway! You're not taking away from those in need, you're showing that this is a real need and should be funde. In addition, you're helping to destigmatize the program; if the kid who gets dropped off in a ratty minivan eats the same food as little Timmy who got dropped off in his parents' 911, that's probably (depending on your worldview...) a good thing.
The big issue I've seen with them is that school cafeterias in middle-class districts aren't sized to feed every student, so you end up with queues long enough that kids who want to get the free food end up missing part of class. The right answer to this is of course to renovate the school and add cafeteria capacity.
