I don't see how anyone could find the death of a great President humorous. You have a sick, twisted sense of humor.
Everyone dies. Sometimes it's untimely. Even presidents. Even great ones. To cope with our own mortality, some of us make light of it. It's called gallows humor. Deal with it.
I used my BB Gun to kill a Behemoth. Just to be able to say that I did. They're kind of fun to use every once in a while, and they're pretty useful early on when you want to get the enemy to go somewhere while you're sneaking (they'll follow the noise of the BB hitting the wall but not where it came from).
Yes, that is the point. Why do you need a BB gun? You don't. Why use it over anything else? Because.
Why even have lower tier weapons in the game? Why not just put the strongest ones in? The answer is variety. You might use a lower tier weapon over a higher one because you like it more.
Me, If I could mod my BB gun into a poisonous high powered killing machine, I would do so.
ALSO, you'd be surprised how accurate high quality air rifles can be compared to their smokeless powder counterparts.