I actually think we should allow cigarette ads again, I don't think anyone is harmed by being able to see a sign telling them something.
But also, think about it this way: isn't this the other side of the slippery slope argument? I'm sure when cigarette ads were first banned, people made the argument that it would be used to justify banning other ads later, and were told that was a slippery slope fallacy... Now, you're essentially saying "we've already banned cigarette ads, if we're not going to ban gun ads too then we might as well re-allow cigarette ads!"
But also, think about it this way: isn't this the other side of the slippery slope argument? I'm sure when cigarette ads were first banned, people made the argument that it would be used to justify banning other ads later, and were told that was a slippery slope fallacy... Now, you're essentially saying "we've already banned cigarette ads, if we're not going to ban gun ads too then we might as well re-allow cigarette ads!"