If my children were crying in a restaurant, I'd do the same thing.
Unless, of course, there were a sign posted that said, "Crying Children Allowed."
If there were a sign posted that said "Smoking Allowed," and I didn't wish to be there under the conditions of the owner, I wouldn't enter the establishment.
Why is this such a difficult concept to grasp for some?
Unfortunately restaurants don't advertise whether they allow smoking or not. If they did and if the economics allowed both to exist, I would probably be fine with that and only visit the non-smoking restaurants. However, you typically don't know whether a restaurant allows smoking until you go there and most do.
I suspect it's sort of like grocery stores with alcohol. If you aren't willing to sell alcohol, you won't have enough profit to stay in business. Therefore once one store in your area starts, all of the grocery stores have to carry it to compete.
I've been in many restaurants that seemed clean and was halfway through a meal only to have a chain smoker light up behind me and ruin the experience. I've turned around and walked out of many restaurants without ever sitting down because their was too much smoke in the air.
Our favorite pizza place allows smoking. It doesn't stop us from going there. But we have often changed our minds about eating in and switched to carry out because of the smoke. Once in the middle of the meal.
I don't really know why they don't compete more on these lines, but I suspect the market forces don't allow it.