It's just the prejudice of your culture.

Imagine how most people have been indoctrinated against drug use. Now imagine how they would feel about your use of cannabis.

This is prejudice, not based on anything logical. Just as some people may never look at you the same when they know you use drugs, so you look down on your friend.

If you are to resolve your prejudice, maybe the cannabis movement stands a chance. As we try to change people's prejudice and longstanding disdain for certain practices, so must you become more accepting of other people's actions/preferences.

Do you accept anal sex or anal foreplay with a girl as the receiver? A female anus is no more built for sex than a male anus.