Specifically, should they become sky-clad Jains, so called because, in traditional India, they went nude rather than kill even a cotton plant, and eventually starved themselves rather than kill even a lentil or grain of rice or wheat?
The question, and the use of the word "kill" with plants, is deliberate, even while also being facetious.
Why? Some researchers have discovered that, at least with peas, some of the claims about "emotions" and "communication" of plants in the controversial 1973 bestseller "The Secret Life of Plants" may just be true.
A lot of vegetarians may have multiple reasons for vegetarianism, often health-related.
But for full-blown vegans, the moral issue is almost invariably the bottom line.
So, seriously and facetiously both, vegans either need to become sky-clad Jains and starve themselves to death, or else get off their moral high horses, if the research yields more such results.
Even if you don't believe that plants have "secret lives," nonetheless, they are alive. So, unless you want to eat either "meat" or "soybeans" out of a test tube, and, in either case, have the substitute made from non-living substrates, not even the algae or whatever that's being used for meat in a test tube now, let's not be so self-righteous out there in vegan-land.
There's more on the "secret lives of plants," even their "foraging" for food, in a follow-up column at the NYT's "The Stone" philosophy page.
The only way you get a partial pass is if you claim the primary reason for being a vegan is earth's natural resources. (That said, livestock raised entirely on grasses, in places that can't readily grow commercial crops, are still then a viable meat source.)
Beyond that, it's clear that some amount of meat protein accelerated brain development among our hominid ancestors, another reason that veganism doesn't necessarily occupy any moral high ground, unless vegans want to pull the food ladder back up after themselves.
And, a side note: I have never practiced veganism, but I have practiced vegetarianism. And, I didn't spend $7 a pound on soy "burgers." I ate vegetarian foods the way they're commonly meant to be eaten. (And, not tofu, either; blech. I ate soy flour as part of baking, normally.)