In July 2019, a bare-chested, pony-tailed man turned up at a vegan market in London, and began snacking on a raw squirrel. In video footage of the bizarre incident, the pro-meat protester can be seen clutching the animal’s limp, furry body – sans head – while a stunned crowd waits for him to be arrested. His mouth is encrusted with blood. At one point, a passing onlooker asks “Why are you doing this?”

This, it turns out, is a deceptively tricky question to answer.

As the popularity of vegan life continues to gather pace, a tide of vitriol has risen. To eat meat, or not to eat meat: the question has become a battleground, with passionate carnivores and vegan activists deploying some deliciously headline-grabbing tactics. There have been pig robberies. There have been defiant public carvings of deer legs. There have been nude protesters smothered with fake blood. There have been provocative sandwiches.

Though it’s natural for people to disagree, the passionate rage – and even mild irritation – that veganism stirs up seems to defy rational sense. Research has shown that only drug addicts face the same degree of stigma – and the least popular vegans of all are those who cite animal cruelty as their reason. Given that most of us would probably like to see less suffering in the world, why is there such resentment towards those who do something about it?

Read more from The Vegan Factor on BBC Good Food

If you dare to ask, veganophobes have plenty of reasonable (and not-so-reasonable) sounding explanations at the ready. First up there’s the hypocrisy argument – the idea that vegans have blood on their hands, too – in the form of plant massacres, the environmental cost of avocadoes, and all the field mice killed while harvesting crops.

But even when vegans are consistent, this also seems to fuel their bad publicity. In the UK, a campaigner recently caused a stir when he revealed that he won’t use public transport, in case it runs down any unfortunate insects.

Other popular arguments include the perception of vegans as over-smug – as the joke goes, “How do you recognise a vegan at a dinner party? Don’t worry! They’ll tell you!” – and over-zealous; a rapper recently cancelled a gig after the singer Morrissey insisted on an all-out meat ban at the venue. On forums, vegans face bizarre accusations like “only psychopaths like vegans enjoy tofu bacon”.

But are these really the reasons that people hate vegans? Not everyone is convinced. Some psychologists take another view – that far from being driven by factors within our conscious awareness, the widespread resentment we have for vegans is down to deep-seated psychological biases.