Well i like to think of myself as a scientist .

Your right that there is no evedance that smoking weed will give you cancer as there hasnt been any tests carried out as it is illigal! Trust me it will give you cancer if you smoke enough of it.

And bongs filter out about 30% of tars and carsonagenics (yes theres a big differance) but they filter out about 40% of the THC so over all there worse for you but not but much.

And yes it is just a suggestion that THC fights cancer, there is no real credible evidance for it so what else can it be but a suggestion?

I have no proof of it but i think that as far as cancer, cigs are just as dangerous as weed, but cigs are physicly addictive which makes them (in my oppinion) a lot worse.

As for that bronchitis thing, that is true as when you smoke the mucus lineing of you lungs surrounds and expels the tars leaveing the lungs open for attack thus resulting in bronchitis and other such infections.