The evidence is there

Today the link between animal products and many different diseases is as strongly supported in the scientific literature as the link between cigarette smoking and lung cancer. For example, subjects who ate meat, including poultry and fish, were found to be twice as likely to develop dementia (loss of intellectual function with aging) as their vegetarian counterparts in a carefully designed study.—Eat to Live, page 101

<idle musing>
But it took about 40 years for people to accept that you shouldn't smoke in public—and cigarette smokers were in the minority! How long will it be before people are willing to accept a whole-foods, plant-based diet? I suspect never! Unless the unsustainableness of the thing forces the issue...
</idle musing>