This is based on the fact that on average, smokers live shorter lives than non-smokers, so they would be paying into a life insurance policy for a shorter number of years, therefore the rate they pay for life insurance coverage needs to be higher.
However, if you quit smoking life insurance companies may offer you a lower rate, after a certain period of time being smoke-free.
For instance, some life insurance companies may lower your rate if you have been smoke-free for 1 or 2 years. If you are smoke-free for 5 years you would pay the same rate (usually) as a non-smoker for your life insurance.
Here's how you can compare non smoker life insurance rates and plans among several leading life insurance companies.