It won't be tomorrow or next week or next year, but it will happen, and it will likely be sooner than we think, imo.
"People over 50 should get most of their vitamin B12 from fortified foods or dietary supplements because, in most cases, their bodies can absorb vitamin B12 from these sources."
I take 2x 1000mcg of B12 once a week. Had my blood tested a couple months ago, I've been vegan over 24yrs and my B12 is on the high end (535pmol/L, healthy range is 150-650.)
If you do your research, you'll find B12 deficiency is actually pretty common in non-vegans too, and many have to supplement even tho they're not vegan.
Try eating "meat alone", I promise you'll regret it after about a week when you have no energy and are completely constipated. They don't 'choose' it, it's their only option much of the year (and they do eat seaweed, some native plants that grow in the warmer. They don't live on ice 365 days a year.)
Plus, you'll need to eat quite differently to adapt - Vitamin C isn't present in cooked animal foods, so you'll need to consume raw liver and brains (or, frozen, as Inuit often do) to prevent scurvy. I'm sure you'll love doing this over taking that B12 supplement. Or are you willing to take Vitamin C daily, but not B12?
Next argument? =)
There are already many charts showing how inefficiently livestock convert resources...per calorie, per calorie of protein, or nearly any other metric, we're much more efficient eating plants ourselves. (And the fact is: we can live without meat, but can't live without plants.)
Finally, just because it's a vegan website doesn't invalidate the resources it links to. The resources are all there, just go through it yourself. (And try not to cherry-pick items that make a thin defence for your case.)
Here, let's just compare dairy products: http://www.motherjones.com/environment/2014/03/california-water-suck
Keep in mind that around 80% of people regularly consume these, and the non-dairy products are a tiny portion of sales..
Here's a collection of articles and stats for those really interested in learning about what's using up California's water: veganstart.org/almonds