They tried that statement recently in Nevada. Turns out that crime has been going down in Nevada over the last decade without changing the drug laws.
Voters don't want crime to decrease even faster?
We'll never know because they weren't asked that question. They were mislead by the statements that "real" crime would be reduced (not reduced faster) if pot were legal.
Reduced faster? C'mon, you're reaching. What if I were to say the WOD is a success because without it illegal drugs would be entering the US "even faster"? Yeah, you'd laugh.