It doesn't affect them much either way but it's not an urban legend. Some smoke is good for them for one. Cigarette smoke is harmful.
you want to debate that... then here we go....
The smoke in general is NOT what is harmful to them, Smoke is made up of a various assortment of chemicals.... The main chemicals being CO and CO2, carbon monoxide and carbon dioxide... CO2 is good for the plants, it is needed for the plants to thrive. CO can cause damage by clogging the Stoma on the bottoms of leaves. When stoma, or Stomata are clogged they can no longer absorb oxygen...
For CO to cause damage to your plants it has to be around the plants for literally minutes. a PROPER indoor room has ventilation which moves air much faster than that..... Outdoors the smoke is dissipated and doesn't cause harm....
With that said, i will say that SMOKE doesn't cause harm to the plants, but smoking in a room that all ready has problems (Such as lack of air exchange...) will cause damage to the plants. wich brings me back to the last post i made...
get a Proper set-up, good lights, good fans... good Genetics and Proven nutrients....
P.S: Nicotine is one of the main pesticides on the market.....