Selling drugs is a federal crime which on its own would merit them going to jail. If you are selling drugs you are promoting drug use that's like saying that a candy company would sell you candy without the intention of you eating the candy. The there are plenty of other things that are perfectly legal to "entertain" someone than doing drugs.
If there are no drug dealers then there's no entertainment for some people and there will be more number in theft and murder. There fore the drug dealers are not supposed to be sent to jail because they sell them to make money and they don't call people to come and buy them drugs