Actually, if your buddy comes to your house, and you want to sell him your comb, that's a private deal. Government doesn't have anything to do with it. Government might have something to do with the tax on your comb when you bought it at Wallgreens. But that's the extent of it.
Why not alcohol or cannabis?
The ONLY reason is, Government takes you to court. And in court they play a game with you that you can't easily win, because they aren't clear about their game.
Lately people have identified 70 major Supreme Court cases that show that Government doesn't have any right in your house and your private deals. It's called Private Membership Association (PMA). The difference is that the PMA is written so that Government can see formally that your deals are private.
The rest is up to you regarding how intimidated you are going to allow yourself to become.
Internet and Youtube search on
Private Membership Association to see that all of this is real stuff that is lawfully being pushed into place by people who are looking for freedom from Govenment PEOPLE who use Government to mess with your private life.

All I said was that you wouldn't have to pay tax on weed if you grew it on your bathroom window. This was in response to this:
Why should you have to pay tax on your own cannabis that you grow in your bathroom window?
If you want to sell or buy it commercially, there need to be laws.
Same as alcohol.