I actually believe it does cause long term harm--but I understand that there are no medical studies to substaniate that.
Really, it's more the alcohol and nicotene. They are very, very harmful to your body, and addiction to them kills people, and ruins people's lives. The people who are hurt by this abuse can be children, friends and relatives of the addict. Not to mention the number of innocent people who are killed by drunk drivers every year. It's dangerous.
BUT, I understand that you can't control everything people do (much as I admit I would like to!) and that people have to have their freedoms. People are allowed to do other things that are potentially harmful or dangerous to themselves or others, it's just a question of where you draw the line. I mean, speeding cars kill people too, so cars could be designed so that they will not go over 75 miles per hour, ever. But the government chooses not to make that regulation. They do, however, have laws about how many brake lights the car must have, and whether the driver can be intoxicated, and whether you have to wear a seat belt, and so forth.
If there's anything we should have learned from the aftermath of Sept 11, it's that there's a very fine balance between safety and freedom.