Why are you vegetarian?

My take on it is simply that it's not necessary, so why do it? I know cavemen ate meat, that's because they had to. But humanity has moved on a lot since then. I'm sure if I was starving I would eat it if there was no other food, but I am lucky enough never to have been in that situation, nor likely to be. It just seems a bit mean for a chicken to die so that I can eat chicken curry, when I could just have a chickpea curry instead.