As an individual concerned with animal welfare, and who eats meat. This article grabbed my attention.
I agree with much of the animal welfare arguments that are presented by Vegetarians, but have approached the solution from a "better care" method.
How To Argue With A Vegan
I know you are correct and touching on a more fundamental problem in society. Each of us needs to be able to pursue what he feels is the best solution to any given problem; unfortunately, some people feel they "know better" (and they might) and feel the need to enforce that behaviour in others.
From that point of view I understand the desire to change others. If you are keeping slaves, I have a desire to free your slaves, and I would think a moral duty. Unfortunately, vegans that believe this are (in my mind) flat out wrong.
Therein lies the argument.