secondhand smoke affects risk. it doesn't cause lung cancer 100% of the time. on a construction site, heavy girders being lifted around cause the risk of one being dropped and smushing you. some things are riskier than others, to be sure.
the problem, sam, is that bartenders and waitresses were not the majority force behind this legislation. it was anti-smoking crusaders; generally, the restaurant industry--and not just the big bosses, but the workers--would strenuously oppose smoking bans (the exception: once a smoking ban was passed in Boston, all the Boston bar owners immediately did perfect 180 turns and began supporting a statewide ban; they didn't want to lose business to outside-of-Boston bar owners. and when MA's statewide ban hits, all those opposed will 180 and begin supporting bans in CT, NH, et cetera).
working at a bar still entails the risk of a drunken customer clobbering you. it's a risk i don't really face at my job here in the library. i hope everyone who gets a job at a bar realises this, and i hope they don't try to make alcohol outlawed at bars because it increases their risk of being clobbered in order to "improve their working conditions".