I do beleive there are other chemicals involved in weed and getting you high, other than just the thc, and tar is not the only bad part of smoking for your lungs, the heat is also not good. Holding hot air in your lungs, is bad for your lungs, holding not as hot of air in your lungs, is not as damaging on the lungs. Nothing in the body likes to be burned. Because there is more than one aspect to what causes damage, it is hard to argue which is worse/better for you, but many seem to agree that bong hits are not harsh, and are bigger hits.