On 9 April 2019, traffic chaos surged in Melbourne while vegan activists blocked Flinders Street intersection as part of a nationwide protest. Police eventually acted, arresting the protestors and throwing them into paddy wagons. Placards were left on the road, their message still visible: “You have been lied to. www.watchdominion.com.”

Widespread condemnation erupted. Prime Minister Scott Morrison dubbed the activists “green-collared criminals”. Greg Sheridan, journalist for The Australian, complained that his “productivity was diminished” because of “vegan militants”.

Even The Betoota Advocate, usually favouring the underdog, took an admittedly humorous swing: “Melbourne’s Vegan Protests Lose Momentum As Activists Begin Napping Due To Iron Deficiencies”, their satirical headline read.

An important message was forgotten among the furore surrounding the protests. That veganism – the belief we should not eat or use animal-based products – has a rational basis. In fact, veganism is based on an uncontroversial moral principle that everyone reading this will accept: that we should not cause unnecessary harm.

So let me carve out the meat behind this argument – so to speak.

Consider why we should accept the principle in the first place. You approach a fork in the road while driving. Road A and Road B are your options. Both have pleasant views, require similar travel time, and lead to your destination. However, driving along Road A causes a boulder to fall from a cliff, killing someone. Nobody is harmed on Road B.

Obviously, everyone would choose Road B. Otherwise you would harm someone unnecessarily. Consuming animal products, however, is analogous to choosing Road A.

Nonhuman animals are sentient – capable of experiencing pleasure and pain – and thus capable of being harmed. We know animals suffer because they virtually all scream, cry or resist when subjected to mistreatment, behaving just as humans do. Backing up this inference, the nervous systems in vertebrates are fundamentally similar to humans.

However, invertebrates – and especially bivalves like oysters – have less similar nervous systems. Therefore, we should be less confident these animals experience pain. Nevertheless, recent research suggests that crabs, prawns and octopuses all experience pain. With the science inconclusive, we ought to give invertebrates and bivalves the benefit of the doubt if killing them is unnecessary.

There is no significant evidence to suggest that plants have the capacity to feel pain.

Killing nonhuman animals for food and clothing causes them harm. Many modes of killing animals do not inflict an immediate death. Instead, they cause animals to suffer greatly as they die. Intensive farming practices confine sentient animals in cramped, unsuitable conditions for their entire lives. Eggs regularly come from hens in small cages, and the male chicks are killed at birth because they will never produce eggs. Dairy products often come from cows who are artificially inseminated in confined barns – their calf taken to the slaughterhouse shortly after birth, leaving the milk for humans, but the mother and calf wailing.

The lives of free-range animals are undoubtedly better than those raised in factory farms. Using them for food, however, still requires killing them. Even hens and dairy cows are killed when their productivity declines, which is usually early into their life span. By killing them, we are eliminating their future pleasures – all for the mere difference in taste between a plant-based and animal-based meal.

So, using animals for food and other items causes harm to animals. We have no good reason to discount this suffering simply because they are not members of the species homo sapiens.

Animal agriculture also produces more greenhouse gas emissions than the entire transport sector worldwide. There are many more negative environmental impacts associated with non-vegan diets. In 2018, Oxford University researchers concluded that plant-based diets are the most sustainable: the “single biggest way” to reduce your environmental impact. For anyone who believes in climate change, the harms associated with non-vegan diets are clear.

Consuming animal products is completely unnecessary for most. According to the American Dietetic Association, “appropriately planned vegetarian diets, including total vegetarian or vegan diets, are healthful, nutritionally adequate, and may provide health benefits in the prevention and treatment of certain conditions.” Granted, vegan diets can be unhealthy, but with proper planning all essential nutrition is available. A plant-based diet may even be healthier as growing evidence connects red and processed meat consumption with higher incidence of bowel cancer. It is no coincidence, after all, that many elite athletes now opt for vegan diets.

There are many delicious vegan dishes too. True, some vegan products are more expensive, but many are not. Lentils, chickpeas and tofu – great sources of protein – are much cheaper than meat-based equivalents. My favourite dish – Spinach Dhal – is cheap, easy to make, and mouth-wateringly tasty.

Therefore, consuming animal-products harms animals, the planet and ourselves. We lack good justifications to cause this harm. It is analogous to choosing Road A.

Other objections to veganism remain. “It is natural to consume animal flesh,” some say, “as nonhuman animals eat each other.” Are other things nonhuman animals do – including torture one another – therefore acceptable among humans too? Moreover, most animals who kill for food would not survive if they did not, whereas we have no need to eat animal flesh.

“We do not actually cause the harm by purchasing animal products,” people contend. “Such products already exist – irrespective of whether we consume them or not.” Nevertheless, there has to be some threshold that – if consumption levels drop beneath – will precipitate a change in ordering patterns. If demand falls for animal products in a supermarket, less will be ordered in the future; triggering a reduction of animals harmed. Vegans, therefore, are not attempting to change the past, but prevent the persistence of objectionable practices. Just as boycotts of products coming from South Africa during apartheid endeavoured to do.

Granted, some days a vegan diet will make no difference. But on other days, refraining from purchasing may cause the threshold to drop beneath the level of profitability. Thus, we ought to avoid animal products. After all, we would all avoid Road A even if there was only a small chance the boulder would fall and crush someone.

Veganism is based on strong foundations – and everyone who accepts the moral principle that we should not cause unnecessary harm thereby accepts the premise of veganism. You may indeed disagree with the Melbourne protests. But a misguided protest does not render the cause itself misguided.

I strongly encourage everyone to watch documentaries about slaughterhouses – to see, for yourselves, the abhorrent reality that underpins our consumption of animal products; hidden from us in the supermarkets, restaurants and clothing stores we frequent. And if you agreed that driving on Road B was the right thing to do, I encourage you to think about how you may be steering the wheel in your own life. On reflection, you may decide to eat like the world depends on it.