if i were to stay here, and develop carcinoma as a consequence of their behaviour, would these people face any consequences for their actions?

and, would that not be a grave injustice? should they not be liable?

but, they would not be. and, no level of liability could overturn the result.

so, how can you tell me that i am over-reacting, when i have no remedy to undo their behaviour?

no behaviour short of knocking down the door and pulling the thing out of the smokers' mouth wouldn't be under-reacting - but all property law exists to protect some type of asshole.