Obviously if more people start using it the number of people smoking it (illegally) in public zones would increase as well (not by a huge amount).
Seeing as I don't want any of those drugs for using myself it's just a nuisance for me (by that small group of people) and therefor a no.
I have asthma and this is definately not the case.
Tobacco smoke would be worse for you than marijuana smoke. (cigarettes have tar, marijuana does not)
And even if everyone in the entire loving world decided they liked marijuana smoking is not the only way to ingest it. (eating or bongs)
Furthermore, if somebody is smoking in a public zone, get away and report them. If everyone followed this course of action people would be hesitant to smoke everywhere they please.