Based on analysis of the teeth of prehistoric man, your ancestors ate whatever they could find and for many individuals it was mainly plants. And your ancestors mostly died young, stole from each other, constantly went to war with the tribe on the other side of the river, did a bunch of abducting women and raping them- as we see that in hunter gather people even today. Very few of your ancestors tried to say please or thank you or not be racist or chose to self sacrifice for the good of the whole. Your ancestors didn't have the level of social organization to build complex machines and in fact killed technical progress again and again by practicing an absolutely stifling level of social control that allowed for no deviation from what the group was doing. Your ancestors believed all kinds of insane religious nonsense that called for excessive adherence to meaningless ritual, even to the point of killing people over it and holding our species in a primitive state for at least 40,000 years.
The key point is that we're in something called CIVILIZATION now, that works much better than what PRIMITIVE man was capable of. And part of being civilized is ethics, where we think about what the impact of our actions is on others. And civilization is supposed to include progress over time, remember that? So, yes, over time it has become mandatory not to be a murderer, or to take the other tribe's corn, it has become mandatory not to treat women and disabled people and gay people and different color people crappily- because we recognize that they have experiences just like we do, and those experiences matter just like we want ours to. We also recognize that a society that behaves ethically also screws ALL of us over less, so it's good for everyone.
The macho throwback caveman thing is very damaging to the work of moving us to a world that's better for everybody. It literally wants to take us back towards a world of misery for everyone, yes even the mythical alpha fantasy men that got to be king or tribal leader for like 5 minutes before somebody stabbed them. The billionaires paying people to push that crap today are pedaling a power fantasy based on the false idea that they aren't where they are now because all of us TOGETHER build the systems that keep the luxury coming in.
Even with its flaws, and our flaws, we live in civilization now. We have science and reason now, and that has given us different information beyond the 'hey seems to me like whatever whatever'. We have learned through science that eating meat is absolutely not required for our health, that in fact it's worse for our health than many alternatives. Yes, if people switch to coke and candybars, that's stupid. But rice, pasta, beans, whole grains, are absolutely not equivalent to sugar. There glycemic index is absolutely not the same. We don't see widespread diabetes in wealthy nations among people eating vegan. Yes, you can point out poor countries like India or other places where some people are mostly eating out of a giant sack of some kind of grain and a giant sack of sugar, and find alot of problems. But that's not the same as a diverse western vegan diet.
There have been a long line of excuses people make for the supposed necessity or eating animals. Before it was 'whole proteins', before that it was some animistic nonsense about capturing the strength of the animals. In India they're hung up on some micronutrient, in Japan they think there's something in fish you'll die without. Science has demolished all of these. Omega-3s aren't as critical as they thought and you can get them better from seaweed anyway. I bet the b12 thing will get disproven in a dozen years, but even if it doesn't there's vegan b12 including in ripe bananas.
The UK and US government and everyone else who has looked at the science has determined that a rational vegan diet is healthy for all stages of life. It's easier on your kidneys, your pancreas, your heart, and especially your gallbladder. And yes, it's a hell of alot better for the planet. And not to mention that, your food will not have died scared and screaming and in pain. (And the plants have feelings thing isn't even worth trotting out, that's very obviously not the same thing. I may as well think my Chevy truck screamed when I wrecked it because the whole car reacted almost like my fender was part of a whole interconnected system!.)....
We collectively make it unacceptable to kill other humans, to be dicks to humans who don't look like us, and to sexually harm each other. That's not some kind of government overreach, that's us all learning and choosing to not be shortsighted and selfish. Animals who don't live free are unavoidably caught up in the net of our civilization just as much as you and I are- they are watching, and feeling, and hoping, and hurting. Listen to the way a dairy cow cries sadly for days when you take away her baby to make veal. Sure, they don't have language or a PHD. But they experience and feel with brains that are really not that different from 90% of our brains. If you don't care about that at all you're either selfish or lying to yourself. Hey, but people are so damn good at lying to themselves....
(Or I guess there's people that really want to live in a mad max kill or be- killed world. Hey, if that's you then please move to Mogadishu and enjoy yourself...!.)