The BBC has a good article on this concept
The tension that results can make us feel stressed, irritated, and unhappy. But instead of resolving it by changing our beliefs or behaviour, it’s quite normal to blame these feelings on something else entirely – all without realising we’re doing it
In the case of eating meat, Rothgerber suggests we have a number of strategies – around 15 – which allow us to avoid facing up to the meat paradox. These include pretending that meat has no link to animals, imagining that we eat less of it than we really do, wilful ignorance about how it’s produced
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Unfortunately, most of these are derailed by the presence of vegans.
According to Rothgerber, people tend not to think of meat eating as an ideology. The dominance of meat eating around the world helps the omnivores among us to avoid the idea that it’s a choice – it’s just what everyone else is doing. But when a vegan turns up at a dinner party, suddenly we’re bumped out of the comfortable “mainstream diet” category and into the unsettling “meat-eating” category. By their mere existence, vegans force people to confront their cognitive dissonance. And this makes people angry.
https://www.bbc.com/future/article/20200203-the-hidden-biases-that-drive-anti-vegan-hatred