Ok, Ill put the tin hat on. Doing this is tantamount to neglect. Smoke, child being sick and choking, not being able to get there in time if some pervert does break in.
In a private home, with the monitor on, and downstairs eating dinner, and no access to strangers, like in a hotel, ok. That is no different to putting the kids to bed and going downstairs. But even to a hotel restaurant, how on earth could any parent actually swallow food not being certain their children are safe. And what if they DO wake up in unfamiliar surroundings, and get scared. Actually leaving the room and even going a short distance to a restaurant is, to me, pretty awful.
If we want to go to dinner, we get a babysitter, or we put youngest in pushchair, oldest is old enough to walk and stay up a little late, and we go together. WE have kids and accept either find good childcare, or take them with, or WE DONT GO OUT.
I think it is selfish and dangerous.