I dont think the constitution has an amendement that guarantees freedom of Marijuana ownership. I think that's the main difference. This is akin to saying that you need a license to drive to why not be required to have an ID to walk around on the streets. The difference is rather simple, one is protected by the constitution and the other isn't.

Also I don't think the consumerist gun ownes commit a lot of crimes with their guns. Unless they are a demographic that is known to be prone to lose or get their guns stolen super often, I don't see how they cause any real issue in term of gun violence. I agree that it is really cringe to see, but they are actually usually responsible in terms of ownership, storage, etc.