Above all, it's an issue for Lex, because the burger needs to be priced not much less than a full entree.
I thought we put this one to bed a long time ago. You convinced me. A full service restaurant with an expensive cost structure needs to make a certain amount of money per entree, hence a burger needs to price that in.
My issue is whether it's worth it. A burger isn't some exotic dish that requires premium ingredients and a high level of skill to prepare. Yes, the Ozersky / Lafrieda myth machine claimed it did but that was marketing bullshit. Since I can get a good burger at a more casual place for about 50% to 60% of the cost of one served at a full service restaurant I don't think ordering one there is a good use of my money. Besides, the reason I go to a full service restaurant is because they serve dishes that require real skill to prepare. I order one of those even though it may cost $10 to $15 more than the burger. To me that's money well spent.
There are people who I respect who occasionally have burgers at full service restaurants. They've got their reasons and I have no issue with them. We all get to order what we want.