I don't have a strong sense of where the lines are, but I do think our accepted standards on violent rhetoric and symbols are pretty incoherent. There are clear terms of violence which are acceptable and in wide use ("throw her under the bus!") and others which aren't. Personally I try to avoid (not sure how well I succeed) all such things, while also trying to avoid freaking out at things which are clearly meant as metaphors. Though it isn't clear what the metaphorical value of gun sights is.
