Yes, this is often a ridiculous situation; or many of those in one. In some cases the option is there to get a half-order, but in most cases that does not seem to be available. And I don't know where the notion comes from to overfill a plate, then leave 1/3 or 1/2 or it to be thrown out. I think, though I'm not sure, that the idea of 'leaving a little' of every item on the plate is based on the appearance that you had sufficient. so your host doesn't worry about it. In eastern countries that is traditinally demonstrated in another way [think Ben-Hur].
All-U-can-eat buffets are alright, but only if you don't do too much watching or thinking about them. It's repulsive to see people horde food onto a plate, whether they actually eat that much or not, in which case it usually has to be thrown out because some will take advantage of the "all..." part and gluttonize themselves there in the dining room and take another 2 meals' worth with them; therefore the rules are set that you do either dine-in or (maybe) take-out, but not both. And kids-- usually there is some little sign up saying children under 10 must be supervised at a buffet, but often they are not, and the restaurant is not going to do anything about it unless they act completely outrageously. Once I saw a boy about 7 spooning a bunch of hushpuppies onto his plate; one fell off and he picked it up with his hand and tossed it back into the buffet bunch. And most people are not careful at all about not touching the food; not if the hunk they want is located in the supply where they will have to reach and their hands may touch what they have to reach over. So much of this is just plain selfishness.
My dad was ridiculous in some of his ways about food at home and many other things. One of the few times he ever used the word "sin" was in the context of "Don't you know it's a sin to waste any food?" After my sister and I were old enough (or so our parents thought) to watch our 2 younger brothers and our grandmother didn't stay with us on weekdays any longer, our dad started having to work different hours, like 4 a.m. to noon, so my sister and I being in charge didn't last that long. But then he took over the cooking, and he always prepared fattening foods and way too much of them, keeping with his "it's a sin..." and complaining that we don't finish everything. But he literally would not listen-- not only was he so stubborn and unchangeable, he was almost deaf in one ear from a WWII injury, and even tring to talk to him could be a miserable experience, with his asking to repeat virtually everything cursing at us for mumbling. I know that the reason I so hate butter is because he would put butter on bread or rolls and put it back in the oven, then they would be saturated on the inside and hard on the outside. But if Archie Bunker had been born a Texas cotton farmer... with that description you would have my dad.
