I completely agree with this. And @Lolamorte comment too.
As another poster said upthread, this sort of "just go and buy more" attitude turns the parent into a slave. Work all day, commute home, open fridge to start dinner, oh I can't because someone has scoffed half the ingredients (whilst ignoring the snack food aplenty purchased for that purpose and requested by them). What now? Back out the door and pound down the road to hope that Tesco Express has what I need, while the scoffers lounge in front of the tv. Fuck that shit, I deserve more respect.
Some of us have a budget. Some of us hate wasting food and packaging and can't/won't buy double ingredients just in case some selfish person decides they want that for their snack and they don't fancy any of the snack foods they actually asked you to buy and just throw them in the bin if not needed. Some of us just don't have time to trot down the road like a Victorian maid to just buy more so the rest of the family dont miss a meal.
Having some very reasonable restrictions in place isn't just about healthy eating, its about family members learning to think about others and the family's resources and values.
Plus some kids just don't self regulate without a firm steer. My younger child is fussy and would literally live on snacks and not touch meals so we do have rules - no more than one ice cream a day and no more than one packet of crisps a day. Otherwise she would live off that stuff (and biscuits), plus she would carry on once no longer hungry. Our older child wasn't like this - which makes me think there is a strong genetic disposition - and we used to be much more relaxed. However younger started getting unhealthy and podgy until we reined it in. I know posters will say I'm giving her "food issues" but childhood obesity IS a food issue. Sorry to use the F word but kids that get fat will stay fat and get fatter. (I did not say that to her obviously, we focused on healthy diet, budget and being more thoughtful about shared resources).