People who want to smoke while eating or after eating can make the choice to stay home and do it, rather than force their exhaled smoke on the general public, and the employees of the restaurant, or they can wait until they go outside.
It is not only rude, but it is endangering the health of the public, to smoke in a bar or restaurant. In order to serve the public, restaurants have to protect them from bad food and drink, they should also protect them from harmful polluntants in the air.