I suppose it's like saying "Well, police killed more innocent people than weed ever did" sort of suggests that weed killed somebody somewhere but the number is lower than that of police. It's just a way of wording things though and only really has that meaning if you apply it to the sentance yourself, but because of how english works the implication is usually there.
It's like the phrase "I'm not being racist, but..." like, you can apply that to like, almost any statement in existance and it's still true: "I'm not being racist, but my cat just had kittens and I wondered if you wanted to have one". Like, it's true, you're not being racist. But when you say "I'm not being racist, but" the implication is that the sentance that follows it will have something that could be considered racist and you don't want that to be taken from it.