Because they enjoy it.
Smoking is a main cause of throat cancer, so to prevent it, I would suggest you stop smoking if you do, or don't start smoking.
The main reason is most likely relious-based bigotry.
There are a number of things that would cause you to gag for no reason. Smoking is one of the main causes as the lungs are affected and are not able to take air as required.
Smoking CAN affect your body wieght. It is more likely one will gain weight if they quit smoking than lose weight, at least in the long-term, if they start smoking. The main reason for this is that smoking increases your metabolism, which is what helps your body burn fat. If you quit smoking and don't replace that with something that increases your metabolism, i.e. aerobic exercise for at least 20 minutes a day, you won't burn fat as quickly as you did when you smoked. Another cause of weight gain for people who quit smoking is that besides creating a chemical addiction to Nicotine, smoking creates an oral addiction, i.e the need to have something in your mouth. Once you quit smoking, people often times replace the oral addiction of the cigarette with food, and thus, eat more.
The main reason for animal cruelty is hunting and to make money. Some people is cruel to animals just for fun.
to survive
Addiction
SMOKING
Unclean environments.
PORN!
people are lazy
so people can learn