Is it wrong that I want my roommate to give up peanut butter?
Why do you want him to give up peanut butter?
That is my favorite food and I don't want him eating it.
I can understand how you might like that as your favorite food, but you shouldn't impose on roomates. They are allowed to like food that you like too. It is good to have boundaries when it comes to things you are willing to share and not share.
It's not like he's eating my dinner plate. I'm asking him to give up the peanut butter so I don't go hungry.
If your roommate is eating your peanut butter, it's necessary to discuss boundaries with him. Let him know that he has to purchase peanut butter so that you both will have enough to enjoy.