The propaganda-machine caters to emotions, not reason, and the idea of a "stronger" drug raises the idea of danger in the casual listener's mind.

Even if this claim were not a total lie, anyone who sat down to think about it would realize that it is actually saying that modern marijuana is less harmful than it was in the past. This is because the only real health issue that doctors can claim as a negative for weed is the fact that smoke inhalation is detrimental to the lungs. A more potent form of marijuana requires to smoker to take in less smoke to gain the desired effect than a less potent variety would.

I'm tempted to write a letter to the DEA posing as an anti-drug citizen telling them that they are inadvertently advertising weed as safer than it was in the past.