I would guess that most people that use marijuana on a regular basis are aware of all of the negative and positive aspects of choosing to use the drug. Marijuana kills is likely not one aspect that would overcome the euphoria that a person gets by using the drug.
When we can see the threat of death, and it manifests itself somewhere other than in our thought process, for most of us anyway, that is when we are going to really think about our decision to use or not use things that are bad for us. It's just human nature, just the way it is.
There are a lot of things in life that we consume, both legal and illegal, that will bring us to this point in time where we have to make the same decision. If we spend our life sweating all of this little stuff, are we truly living?