Imagine that to avoid animal suffering required a wholly artificial diet - perhaps one synthesised in a replicator like the ones in Star Trek. Let us stipulate that the amount of pleasure experienced in the eating of such food is exactly akin to that currently involved in eating good quality vegan cooking. In that case the answer to 'is it necessary' might be yes, or might be no - depending on what you mean by necessity. But would we be ethically required to adopt this diet?Dom says "Absolutely!" The residents of my house said "pass the salt!"
Well. I will just say--there are two questions here. Pollan is worried about two links being broken: (1) The link between food and nutrition. He says "no" to vitamins, supplements, fortified foods, etc. Food should be nourishing. That's a problem for a vegan diet that has to be supplemented with lab-created B12. (2) The link between food and the natural world--you know, sun, soil, grass, crops and such.
Here's how it's all supposed to work, according to Pollan: the earth yields food in a natural way and then food nourishes us. If you let all that happen in the old-fashioned way, the whole thing isn't pain-free (field mice are killed by combines, chickens are killed, etc) but there isn't the perversity and misery of a factory farm or modern slaughter house.
In Dom's thought experiment, one of these links is broken--link #2. Food doesn't come from the natural world in the normal way. Yet nutrition does come from food. So, the replicator is bad (in one respect) from Pollan's point of view, good from the point of view of reducing suffering.
I do argue in both of my books that pain and pleasure are not all that matters. But they do matter a lot. So it's not an easy thing to argue that Pollan's scenario is preferable. (In short, I'm thinkin' on it, as we say in Texas.)