I'm kind of on the fence when it comes to this topic.  I personally do not use marijuana (though I did so many years ago in my younger days).

On one hand, I personally don't care what people do in their personal lives and/or in their homes.  If someone wants to smoke a joint to relax after a day of work or while socializing on the weekends, I don't see any problem with that.

On the other hand, I have heard of and seen cases where people are smoking marijuana while on break at work.  This includes places where dangerous machinery is used and regardless of my personal opinion of marijuana use, a person should not be operating machinery, driving, etc. while impaired... especially on the job.

To go along with that, at the place that I work at we handle classified information and have to have a security clearance.  A person that can't pass a drug test displays poor judgement and therefor cannot hold a security clearance.

---