There's a difference between supporting a free and peaceful drug trade and participating in a very-much illegal drug trade.
It's possible to be a hemp-wearing, tree-hugging hippie and be pro-death penalty - it also happens to be rare.
Do you have any statistics to back this up, or just the naive reasoning "Well, it's a /serious/ crime, so they'd probably commit others, because only bad people commit /serious/ crimes"?