Bizarre little statement. No less so for being a fairly common sentiment.
If marijuana is harmless, why tax it differently than bread? If harmful why legalize it?
I think the obvious answer is that marijuana may not be terribly harmful (at least that's the legalizers' position), but it certainly is addictive. Legalizing it will produce great tax revenue because, to the addicts at least, it is a necessity. Regardless of the tax burden they must continue to buy.
Seems to me more of an indictment of the morality of "sin" taxes (those on alcohol, tobacco, and gambling), rather than an endorsement of anything regarding marijuana.