I wonder how many vegetarians (including vegans) became so as a result of activism and how many came to vegetarianism more naturally. I reckon that a spontaneous shift to vegetarianism is very psychologically different to the preached variety.
Spontaenous vegetarianism comes by the liberation of true meat-avoidant feelings from lower factors such as peer pressure and ego. For contrast, preached vegetarianism could mean the suppression of true meat-enjoying feelings for the sake of these lower factors: pressure from others, the ego-boost of shifting to the logical/approved/1337 side.
There are already enough pressures telling us how to behave coming from others (and The System) floating around nowadays. More preaching is the last thing the world needs. All one should need to become vegetarian is good inner quality, an environment that will allow this quality to express itself (this includes the mental environment) and exposure to the idea of vegetarian cooking.
Anger is not the way. Besides, for now it is impossible to judge inner qualities as man is blinded by his busy mind. Preaching keeps the minds even busier; they ought to be less busy: that energy should be directed towards the heart. The better approach is to simply cook and share vegetarian food with people (in the short term), to free peoples minds and to help free them from their minds (in the long term) and to eventually raise the standards of humans being brought into this world (in the endgame, by sexual selection NOT transhumanism).