For me that's a mix of ethical and environmental concerns.
I agree that there is a point in the belief that it is unethical to kill animals. That's not the most unethical thing that is happening in the world, there are a lot of things to argue about, but in general, I agree that in an ideal world, we should not do that.
The environmental concerns, I only buy half-heartedly. I don't really believe that land-owners will transform their pastures or soy cultures into rain forest instead of another profitable exploitation, I'd rather have states force responsible production and norms.
It is just not practical for me to go full-veg, where I live I would need to cook one hour a day for it, and I am a lousy cook, I have neither the inclination or the motivation for it.
But I reduced my consumption more and more. It was surprising to see how my taste changed. I used to be a huge meat eater and now I find eating even a small steak a bit nauseating. I almost eat no beef anymore, little pork but mostly chicken and fish, and even these I eat little.