My take on this is that everything I have found so far (apart from stuff by the Weston Price Foundation) indicates that a plant based diet is healthier. However I tend not to believe the latter organisation, for reasons I have posted before. I think the deceased Weston Price himself was OK though.
I know there are some arguments to suggest we may have a few deficiencies if we stick to a vegan diet, but I am wondering if those deficiencies are caused by other things we do wrong, for example repeatedly washing our hair and body with petrochemicals, thereby making us excrete more oils than we would naturally to replace the oils we wash off, which I understand contain omega 3 oils. Similarly B12 is in bacteria on plants, which we get rid of when we wash the food to remove the petrochemicals such as fertilizers and insecticides, thereby throwing out the baby with the bathwater. It might be that if we lived more natural lives, these deficiencies that can sometimes occur with a vegan diet would be addressed.
It would be nice if we could survive on a plant based diet. It doesn't feel restrictive to me, and plants etc are a delight to work with in the kitchen. I have no worries about bacteria from fish and meat. If I drop a carrot, I end up with a dried carrot, not a deadly bacterial culture. Apart from that there is the cruelty to animals. Ad I am not talking about catching a fish with a hook or killing a wild animal with a weapon. I am talking abut the insane methods of "farming" animals we have now, filling them up with cocktails of drugs and forcing them to eat unnatural food in prison camp like conditions, the sort of thing that makes them unhealthy and poisonous to us. Plus these practices are unsustainable in the long run, so one day we will have to change. Videos such as those showing how Dr Caldwell Esselstyn reversed his colleague Dr Joe Crow's heart disease, and a testimony from a university professor in Wales to me are incontrovertible evidence that very low or no meat or dairy is the right way to go.
On the other hand I have friends who give me the "everything is OK in moderation" mantra. I used to agree with that, but I don't now, because I know more information. I think we have all been dumbed down by the way we are brought up, and what we have gotten used to. For example think of cigarette smoking 50 or 60 years ago. Now it's not OK to have cigarettes in moderation, or even passively smoke. In better times your ancestors would have known what's good and bad, that knowledge would get passed down the line, and this is why we all survived as genetic successes. With our artificial society we have cut ourselves adrift from that essential knowledge. In the West we are now guided by subliminally influential television adverts and questionable "experts" who are financed by big businesses, with the sole interest of making us part with our money. Result? cancer, strokes, heart disease, and a booming pharmaceutical industry to boot. Is this good health? I don't think so.
Look what happened when Germany invaded Norway in the 2nd world war and took away their animals. Heart attack rates plummeted, and went back up after the war when they re-introduced animals.
Anyway my current view is that it's probably best to have nil processed food, farmed meat or dairy, and an optimum diet would be locally grown organic seasonal fruit and vegetables, cos that's what we have probably lived on for thousands of years and our bodies are geared up to it. However grass fed or wild animals are probably OK, and healthy fish. But I have a sneaking feeling that a vegan diet can be 100% healthy and best for us, if we stop doing other silly things to our bodies. I think there are other factors in the longevity and health mix too, such as mental attitude, happiness, relationships.
The bottom line is I don't mind if people choose to eat meat, dairy, junk food, carbonated drinks, burgers, whatever. It's their lookout, not mine. All people can do is try and eat what they think is best for them, but to find out what that is I think you need to have an open, impartial and inquisitive mind.