This isn't necessarily true, except in the strictly mathematical tally of "calories". It's a measurement that isn't actually useful, because those calories don't necessarily have a better purpose than feeding meat animals, and don't necessarily have a cost or opportunity cost associated with them. Also by simply counting the calories you're ignoring other impacts of the system.
You actually don't have to kill any plants to feed livestock. Ruminants can get their requirements from a patch of grass and then move on to another without killing the plant, similar to a lawnmower. If you're killing the grass, you're doing it wrong.
It's not a waste unless those calories and water would otherwise go to a useful purpose AND there are no other benefits created by the system. Neither of these is always true. One example is animals raised on land that can't sustain crops, due to elevation, soil quality, terrain, etc., but can sustain plants on which animals can be raised (most of the world isn't flat, fertile, Midwest farmland). Another example is cattle raised on pasture in a manner that contributes to the healing of the land. Well-maintained managed grazing operations can add topsoil, increase biodiversity, reduce waste runoff, sequester carbon, and more.
Ok, so? You weren't going to eat 1,000 pounds of prairie grasses, vegetarian or not (hint: you can't digest the same things a cow can).
Depends where they're getting their meat from, and how it was raised. So for most of us in America, maybe so. But it doesn't have to be this way; there are alternatives.
The points you mention here are indicative of a classic American problem of hitting the wrong target. There are many problems with eating meat in our current food system, and it's natural for people to object to them. But they aren't inherent flaws of eating meat, rather problems with the system that created that meat. It's a failure of logic to conclude that eating meat is the problem, when the problems lie within the system. If you don't like industrially-raised beef, then don't eat beef raised in that manner. There are alternatives out there.