Humans are extremely adaptive animals; that's why we're "omnivores" in the first place. It's effectively our modus operandi to eat whatever the hell is around us that isn't directly poisonous, and even some of the stuff that is.
As a result, anybody trying to tell you what a "natural" or "unnatural" human diet consists of is pretty much full of it. Human diets have varied so much across space and time that the options you actually have, especially in a modern society, are pretty amazing. I mean, you have some forms of vegetarian stretching back centuries, and on the other hand, you have cultures like the Inuit who had to figure out how to survive using essentially no plant products at all (which requires some pretty interesting dietary habits and rituals of their own).
I don't really think every vegetarian/vegan in existence expects the entire world to share their dietary habits; I think most of them are smart enough to realize that this isn't remotely possible at this point in time and that the choice to not eat meat (or animal products, as the case may be) is only possible because they're lucky enough to be in a position where they can feasibly make the choice.
For the most part, what humans "crave" as food depends on what we're used to. Some cultures eat insects, but if I see insects (even ones eaten by some other people on the planet), I don't reflexively think of it as "food" even though there's nothing really wrong with doing so. Many vegetarians, after not eating meat for a long time, actually find themselves disgusted by it rather than craving it, because they don't quite see it as food anymore due to a lack of exposure and the decision on their part not to do so.
There is no constant and unchanging part of the brain causing you to crave every single thing that might be food. Humans naturally eat meat, yes, but that doesn't mean that choosing not to is somehow irrational. Otherwise, it would be irrational for any of us to wear clothing, use an alarm clock, grow staple crops like wheat (which don't even exist naturally), or any number of other ways in which we either subvert our natural inclinations or condition ourselves to have inclinations we weren't necessarily born with.
You don't have to be rich to be vegetarian, especially because a salad costs less than a steak, and you can very easily SAVE money by avoiding meat.
This is a pretty bad comparison. Salad and steak (for most salads, anyway) do not share remotely the same nutritional role. They are not substitutes for each other, and no vegetarian (and nobody who studies nutrition) would claim that they are.
Your thinking is jaded because you live in a society with economy. Think of yourself as an animal because that's exactly what we are when considering basic needs. As I have said, pound by pound, meat give more energy then vegetable. This is a fact. Thus, given the choice between equal amount of meat and vegetables, meat is always a better choice for survival reasons. The 4 thousands years or so of civilization caused little changes in bodily needs comparing to the 6+ millions years of evolution prior to discard the latter.
This assumes that an equivalent mass of meat vs. "vegetables" costs the same or is otherwise equivalent. This is hardly ever the case. Which one you'd choose depends not only on what kind of vegetable it is (you realize there's more at stake than calories, right?), but how much of each is
actually available, and especially in agricultural societies, you're going to have a lot more vegetable matter than meat, especially staple crops like grains.