I know tons of vegetarians and vegans who aren't pushy or obnoxious at all about their choices. There are some raw-food-diet people in my community who get on my nerves, though, as well as some people who will treat you like a pariah if they find out that you ever eat a fast food meal, or if you sometimes buy some things that aren't organic, or if dessert is eaten. It's all about boundaries, so even though I agree that minimizing meat consumption is good for people individually and collectively, I also love a nice steak once in a while.
As for the story, there are so many things that can cause cancer, where do you draw the line? For example, grilling foods causes carcinogens to form in them. Should charcoal bricquets come with a warning? Should grills have a big label on top telling people about the cancer risk?