Drug tax stamps

This is hilarious. I was trying to find out WHY there are drug tax stamps for marijuana (and other drugs). While I was searching, I found this website:
http://www.ksrevenue.org/perstaxtypesdrug.htm#top

It explains how drug dealers in Kansas can obtain tax stamps for their marijuana. Why the hell would a drug dealer do this? It says that the dealers info can’t be given to law enforcement, but I doubt that is true.

If it is true, isn’t the government sending 2 different messages? Marijuana is an illegal drug. Yet, they have stamps for it, which have to be (supposed to be) with the marijuana when it is sold. I have never personally seen a marijuana tax stamp. It’s just stupid!