I don't know that there is a smoking dentist out there who claims to be oblivious to its effects or that their working and home lives are completely seperate. Dentists of all people know what the effects are. I think it's mostly a matter of addiction, and partly a matter of informed people knowing the consequences of something and choosing to do it anyway.
So it can be argued from both sides. I personally would feel horrible being a smoking dentist, but I'm sure that healthcare providers are scrutinized more than many other professions for practicing what they preach since they are constantly educating and "demanding" practices from the public. So I'm sure I"m doing many things that my future patients think I shouldn't be doing!!!