Not exactly correct. The biggest decline in smoking was the result of conclusive proof of the direct, lethal effects of smoking and the subsequent prohibition on marketing tobacco as a healthy product and doctors dropping it from their prescription list. The cultural decline has happened a lot more slowly.

That said, comparing tobacco to guns is like comparing cocaine to rat poison. Nobody ever thought rat poison was great medicine or misunderstood that its most effective use was killing rats. Guns are intended and designed for killing. I don't think that's broadly misunderstood. The whole reason there's an amendment ensuring people can have them is because guns are good for their intended purpose.