With the emergence of meat-free meats as a mass consumer option via fast-food outlets like Hungry Jack's and an increasing diversity of meat-free products in supermarkets, even the trivial objections to ceasing to use mammals as a food source have now vanished. The shuttering of the livestock and dairy industries would be a sensible policy goal in any polity that actually embraced, rather than simply spoke about, evidence-based policy.
Meat and dairy are monstrously cruel, poorly regulated industries, even if you're OK with the ethics of killing intelligent, social creatures of the same animal class as us for the production of meat and milk that we don't need to consume. And even if you're OK with mammals being killed, abused and immiserated for your taste buds, the environmental impact is frightening: while livestock's climate impact has been overstated, it is still a major source of greenhouse emissions worldwide and only likely to increase as incomes in developing countries grow, bringing meat into the diet of more and more people.
Beyond those, there remain only trivial reasons for not ceasing to eat meat, mainly around special dietary needs that can be addressed through supplements, and the diversity of substitute products on offer for those who refuse to subsist on vegetables, free-range chicken and sustainably sourced fish. As the humble Not Burger is being supplemented in supermarket freezers by products that, with greater or lesser degrees of success, mimic the taste and texture of meat, that reason is vanishing. And as a greater variety of non-dairy milk products become available (with soy milk probably being the least worst in terms of environmental impact, given almond milk production relies heavily on water consumption), continuing to consume dairy milk also becomes an egregiously unethical act.