Saying that smoking weed causes no health problems at all is complete and utter bullshit.
Smoking ANYTHING is bad for your body.
Even if you smoke just cannabis you're bringing shit into your lungs.
We all know it's fact.
Lung cancer is primarily caused by smoking. So yes, you can say Cannabis has been the catalyst for a persons demise in that respect.
As for what cannabis can do to your body, disregarding the smoke inhalation..fancy a bit of Paranoia, short term memory loss or perhaps the worst psychosis?
Hell, I love smoking weed but It pisses me off when people don't realise that cannabis DOES have negative effects if it is not used in moderation.
Just like everything else in life.