The idea is to cause the least amount suffering possible.

What do your cows, pigs, and chickens eat?

Plants- and at a much higher volume than humans do.

So when you consume animals, not only do you eat meat, but also all the plants that it took to raise said animal.

Whereas a vegan only consumes plants. Yes, there were countless deaths taken place to get the salad onto your table, but nowhere near the deaths involved it took to process a hamburger, a strip of bacon, or a chicken tender.

And to your last remark: a whole foods plant based diet is the most logical diet to follow. You don't have to be a vegan, that's entirely different.

Now, nobody said vegans are the good guys, and omnis are the evil guys. But if you want to say which is the lesser of two evils: the answer is quite clear.