Well, my DS and DDiL think it important, they have been more relaxed than I was, but we have been able to take DGC out to proper restaurants to eat since before they were 5.
I am not sure it is such a new problem. I can remember, in the mid-1960s, walking out of a restaurant because a child, around five, on the next table was spreading food all over the place, eating with her hands and then putting them in the sugar bowl and I felt quite ill. I was in the Harrods Salad Bar at the time, as I worked nearby. I can also remember children running wild in decent restaurants back then as well.
Many children today are used to take-aways, but never eat out, not even in a McDonalds. In the past when parents had to cook and prepare all their meals, it was more efficient to sit round a table and eat the same food at the same time, with all the benefits that engenders. Now too often, everyone in the family, even children, get the ready meal they want out of the freezer when they want it and eat it wherever they please so that food is no longer a family meal but a bit like going to a garage to buy a fill of petrol for the car.