Why Is Smoking Legal?

Smoking is mass murder. From the National Cancer Institute:
"In the United States, secondhand smoke is thought to cause about 46,000 heart disease deaths each year."
"Approximately 3,000 lung cancer deaths occur each year among adult nonsmokers in the United States as a result of exposure to secondhand smoke."
"There is no safe level of exposure to second-hand smoke."

From the California EPA's 1997 report on second-hand smoke:
"50-58 percent of SIDS cases nationally (1,868-2,708 deaths in 1993) may be attributed to ETS exposure" (chapter 4, p140). (ETS = environmental tobacco smoke.)

That's over 50,000 deaths of non-smokers a year in the US. Why is smoking legal?