I describe myself as a vegetarian and I am a natural one. I was born that way and have not been able to eat meat since I was weaned from milk as a baby.
Over time I have learned to eat bits of white fish and chicken breast, flakes of salmon, but if you were like me growing up in the '70's not being able to stomach flesh, well it was a very unpleasant way to be.
Attitudes weren't as liberal as they are these days and when I was little other people assumed that I was the child of controlling hippie parents and would load my plate with grim meat.
It is worth using the term to mean non-fish-eaters though. While I can handle flakes of it, I am often given whole fish at BBQs with bones (boak) and skin (boak) Cats love me 
I don't know why you're angry at people who say they're Veggie but eat fish of any kind though. I wish I could, in fact I wish I could eat meat full stop. It doesn't bother me much these days but when I read a post like yours I do feel a bit sad because I can't help the way I am.
No disrespect to people who choose not to of course, that's your prerogative, I'm just putting forward the opinion of someone who has no choice and had a bit of a shite time with regards to food when I was a child thirty years ago.
And wonders why it riles someone who (presumably) can easily eat any type of food without feeling like a social outcast.