No safe level of exposure to tobacco smoke.  It’s suprising to me how long our society has taken to get to the point we’re at on cigarette smoking.  Freedom of choice is important to me so I’m first inclined to step away from the issue and say that people make their own choices.  Unfortunately the consequences of their actions impact society as a whole through increased medical expenses stemming from diseases that were preventable.  I realize the addiction aspect of the habit but denial of the potential outcomes won’t get you out of the cancer treatment that your future may hold for you if you don’t quit.  Here’s a great write-up on it from CNN:  http://www.cnn.com/2010/HEALTH/12/09/tobacco.risk/index.html