I do agree with some of what Daniel5 has said - it is because some vegetarians take preaching too far. Sometimes they can be too critical of others and their beliefs, and think things are black and white when they're not (sometimes I see it on this forum as well).
Although I'm vegan, I find PETA extreme and idiotic as well (they do good things, though, but there's a LOT I don't agree with). It's those sort of vegetarians that ruin it for the rest of us, and make many meat eaters hate them and think all vegetarians are aggressive.
However, I think it's the meat eaters who are more aggressive. I never give people shit for eating meat, but MANY people try and argue with me about how veganism is stupid -- so yes, they still do hate us initially despite the fact that some people do not preach (but they don't personally hate me when they realise I'm not like that). The Sam Kekovich ads were saying how idiotic vegetarians were, and how we were un-Australian for not eating meat. Can you imagine what kind of negative response us vegetarians would have gotten if we'd done a similar ad blasting meat eaters?! We evolved eating meat, so technically veganism could be deemed unnatural in comparison, but I think people do not understand the atrocities that are committed in the meat, egg and dairy industries. I can see how some people compare fundamentalist religion to preachy veganism -- it has similar traits. But in reality, meat eaters are far worse in their preaching I think.
I think the more of us who can show people that not all vegetarians/vegans are preachy or extreme, the more people will realise that vegetarianism is not as extreme as it may sound

We shouldn't be persecuted for not wanting to contribute to the awful industries our society supports. If you're not, "OMG YOU'RE A MURDERER IF YOU EAT MEAT!!111!", people are more likely to listen to you.