Of course he should. If he wants to. This isn't "There's only one way to feel about Cannabis.com."
I'm one of those people for whom it negatively affected my motivation and memory very noticeably. It also affected my heart rhythm in a frightening way and, if I used it now, would likely interact with the anti-arrhythmic medicine I take. So I abstain as well. I want to use it again later, and I really want it to be legal when that time comes. I like the way it feels and I found that, for me, although it depleted my motivation, it still did good things for my mood.
One of the things I always cringe at here is when one person tells of his experiences with cannabis and others jump in to tell him he's feeling the wrong thing or saying the wrong thing. Or that his personal experiences are somehow incorrect, all imagined, or invalid. If I could have a single wish granted for this site, it'd be for people to realize that cannabis affects different people different ways, not all of them positively. Just because it affects four people positively doesn't mean it does the same thing for the next four. It's like any other medicine. People are going to have both negative and positive responses to it, and that's as it should be since every person's body and neurochemistry are unique.
Anyway, that's my message. Live and let be. Let freedom ring. Let cannabis be discussed in the first person as people experience it and don't step over those boundaries and tell someone he's wrong for not feeling the same thing you feel. We'll be doing a heck of a lot more justice to cannabis if we acknowledge that it works well for some and not for others than pretending that it's the be-all end-all substance for everyone.