Do you know why people use meth?As for making drugs safer after legalization you are correct. That however doesn't change the nature of the drug itself and its ability to addict and or reduce its addict to a walking skeleton. If made inexpensive by legalization I bet there are going to be even more people looking like a walking bag of bones. Cheaper only means more money for the drug. At some point the stealing and other crime will begin again.
Because the softer drugs aren't any easier to get, and meth is easier to smuggle than pot and more profitable on a per-dose basis. The meth epidemic was created by the prohibition of less extreme drugs.
I have never used pot (or any other illegal drug); the hardest thing I've ever used is hydrocodone cough syrup, at the prescribed dose. I used to be a convinced "drug warrior." But I've come to the realization that our current war on non-approved herbs is idiotic, especially the war on the cannabis plant.