I can't say I agree with this sentiment. This sort of thing happens in other food service outlets and it's never bothered me. The one that comes to mind is grocery stores having separate slicers for meat and dairy to accommodate those who keep kosher. I'm not Jewish, and neither am I a vegetarian, but I wouldn't call those who do keep such lifestyle choices unreasonable.
Also, the word demand here commands more than one meaning. If there is demand for such a separation, and money to be made from accommodating that demand, those practices will find their way into the market.
Look it, no one is demanding anything. They're mis-representing their product. That's all that I'm saying. The end.
Everything else you're saying, your railing against the so-called "vegan moral framework," etc..., is, to me, just you grinding an axe.
They are flame broiled, not grilled. They aren't cooked in any type of grease.
Many fast food places (McDonald's, Wendy's) use a flat surface similar to this:
https://upload.wikimedia.org/wikipedia/commons/c/cc/Flickr_X...
Typical ground beef is 20% fat (80% lean), and if you cook it on that, the fat will melt, it will hang around on that surface, and whatever else you cook next will be cooked in animal grease left over from the beef patty.
If you flame broil, the burger sits on a wire mesh, and the grease drips away.
I'm not just picking nits. I'm really trying to make a sincere point that I think one method will have significantly less transfer (not zero) than the other.
They are fairly large and probably expensive, so a separate broiler may not be an option.