Yes, this topic has been discussed many times, but not everyone reads all the previous discussions, so I'm going to repeat what has been said before.
First, if you do a poll of people and ask: "Are you a vegetarian?" you will get about 7 percent of the population in the US saying "yes." But if you do a poll on the same population and ask specific questions about their diet, like, "Do you ever eat fish? Poultry? Pork?" etc., and then tabulate the results for the correct meaning of vegetarian, you will get about 3 or 3.5 percent of the population. Put another way, roughly half of the people who describe themselves as "vegetarian" are using the word in a way that differs from the dictionary definition. That's just a fact of life. Perhaps, instead of becoming angry, it would be better to deal with this as a fact of life.
Second, since dictionaries published after WWII tend to say they are descriptive of language usage rather than prescriptive, then it may be only a matter of time before what is now the non-standard usage of the word finds itself included in the dictionary as an accepted usage. I don't see any way of controlling or stopping this from happening. And words like pesco-vegetarian and pollo-vegetarian are already finding themselves included in some dictionaries.
Third, I think the comments about the word "meat" are off-base, mostly because they assume that the word "meat" has only one meaning. It does not; it has multiple meanings. If you look it up the word "meat" in Webster's On-Line dictionary--which is not even an unabridged dictionary--it has five different numbered definitions for "meat," with a number of lettered subdivisions, so eight if you include the letters. And even the lettered subdivisions could be further divided. So there are at least eight different meanings of the word "meat," possibly more.http://www.merriam-webster.com/dictionary/meat
The word "meat" can be used, among many other meanings, to mean the flesh of mammals. See 2a: " also
: flesh of a mammal as opposed to fowl or fish." The formulations of the early vegetarian societies in Britain in the latter half of the 19th century said vegetarians abstained from "flesh, fish and fowl." "Flesh" was used to mean the flesh of a mammal. Hence the need to include "fish and fowl." "Flesh" in this sense was used as synonymous with "meat," which again was used to refer to the flesh of a mammal.
This usage of the terms "flesh" and "meat" approximates the Catholic usage of the terms when they talk about the abstinence from eating "meat" on Fridays. They are referring to the "meat" of mammals and birds, i.e., warm-blooded animals.
"Meat diet comprises the flesh, blood, or marrow of such animals and birds as constitute flesh meat according to the appreciation of intelligent and law-abiding Christians. For this reason the use of fish, vegetables, mollusks, crabs, turtles, frogs, and such-like cold-blooded creatures is not at variance with the law of abstinence. Amphibians are relegated to the category whereunto they bear most striking resemblance. This classification can scarcely preclude all doubt regarding viands prohibited by the law of abstinence. Local usage, together with the practice of intelligent and conscientious Christians, generally holds a key for the solution of mooted points in such matters, otherwise the decision rests with ecclesiastical authority."http://www.catholicity.com/encyclope...bstinence.html
It is basically a misunderstanding of the usage of the word "meat" to suggest that Catholics are using it in the same sense (when they talk about Friday abstinence) as are vegetarians when they talk about abstaining from eating meat.