The stupid thing is that there are already plenty of good arguments for being vegetarian, or at least dramatically reducing your consumption of meat. Among those: health and longevity, reduction of pollution (greenhouse gas emissions, agricultural runoff, overuse of pesticides, herbicides and fertilizers), reduction of the overuse of antibiotics contributing to antibiotic resistant bacteria, reduction of water usage, reduction of deforestation, reduction of overexploitation, the ability to sustainably support the world's population, etc. These don't involve accusing people of murder or making really dubious and unfounded claims. Pragmatically speaking, there would be a much larger benefit to taking a milder stance and convincing people to reduce their meat consumption by 50-75% or whatever. I don't know why anyone would think this kind of fanaticism does anything good for the world. It's certainly not going to win anyone over.