Today's generation just blindly accepts what is given to them and at most shrug their shoulders and make a simple tweet or remark:
It's like going into Taco Bell and say to the manager 'HEY! Your burrito sucks!!!' and he can rightfully say 'So do you bye bye!' where as a proper way is saying the burrito didn't come at proper temperature/not enough or too much ingredients (though usually the former) and the kitchen you see is a filthy mess please clean it up ASAP!.
Enough customers pointing it out the manger will HAVE to fix it or risk getting fined/shut down.etc which then Taco Bell Corporation may say 'Well nobody likes Taco Bell' which isn't exactly true. Nobody likes dirty kitchens!
If the manager just constantly hear 'Burrito sucks' it won't help him to know where the problems lie before he eventually gets inspected if he is in an area that regularly enforces such things.
Something that gets lost in these discussions is whether or not someone has the authority to respond to criticism.
If you complain that your food is undercooked the odds are that someone didn't follow the procedure for ensuring the food is properly cooked, so the manager will have some authority to investigate whether or not the procedure was followed (not whether or not the procedure was correct). If you complain that there's not enough beef in your beef taco, there's nothing that manager can do because he doesn't have the authority to change the recipe to add more beef.
"Constructive criticism" is only useful and valuable when the person you're giving it to has the authority to respond to it (or relay that criticism to someone who does). Otherwise it's wasted effort. The problem we are running into now in our Managerial system is that this responsibility is so diffuse that no one has the authority to respond to it. To add more beef to a taco there will be double-blind taste tests and focus groups and marketing studies and beef pricing reports and process change studies all fed into an "advisory committee" who will make a "non-binding recommendation" to someone who has probably never even seen one of these tacos in-person let alone eaten one who ultimately has the authority to change the amount of beef in the taco.