Perhaps you’ve already seen the advertisement: the one with the naked silhouette emerging from the swimming pool, the panpipe soundtrack, and the breathless voiceover . . . “Nothing in the world has changed me as much as this, I feel so much better . . . it’s so amazing!” I’m not talking about Alicia Silverstone’s “GoVeg” campaign (sponsored by People for the Ethical Treatment of Animals and predictably banned by a cable company in Houston), but the rival “GoMeat” campaign, featuring the naked torso of an overweight Mexican security guard, Guillermo RodrÍguez.

The ad made its debut last week as a skit on a talkshow and sums up the feelings of the majority of Americans about vegetarianism: if animals weren’t meant to be eaten, why are they made out of meat?

And yet meat-eating, like every other great American tradition – such as burning gasoline and buying houses with dodgy mortgages – is under attack like never before. The newspapers are full of obesity statistics (the national obesity rate is reported to be an astonishing 32 per cent) and Newsweek has assigned an unlucky correspondent in New York to live as a “freegan”: someone who eats food that has been or is about to be discarded. This is not as impossible as it sounds: some 90 billion pounds of food is thrown away in the United States every year.

Like many people, I am wildly schizophrenic on most of these issues. For example, I have no problem with “meeting my meat”, as the GoVeg website encourages you to do. When I was growing up, I made friends with the cow that lived in the field behind our garden, and it failed to put me off the Sunday roast. And yet the thought of mass factory-farming, like mass factory-anything, makes me want to eat lentils.

Then again, there’s something equally disturbing about this recent trend of mass self-loathing that has reduced every facet of human existence to an example of how our rapacious consumption is laying waste to the planet. Say what you want about a bacon sarnie, but nothing can quite match the strain on your cardiovascular system like the feeling that you’re single-handedly responsible for the coming apocalypse.

Which brings me back to the vegetarians and the freegans. Both are noble causes. And yet trying to capitalise on our self-loathing is dangerous. Believing that killing a chicken is the same as killing a human is one thing. Bundling it in with the suggestion that an obese woman will look like Silverstone after she “goes veg” is another entirely; as is the suggestion that vegetarianism will solve the world’s energy problems. As for the freegans, you’ve got to admire the commitment. Still, wouldn’t all that energy spent foraging be better used trying to work out how to make electricity from sustainable natural resources?

Guilt, after all, never solved anyone’s problems. It’s usually optimism that does the trick – and Americans used to be good at that.

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