Yeah, that sounds really good until a bit of distance is added. The longest shot in my house is 18 yards. Birdshot is going to be a piss-poor deterrent at that range...or 15 yards...or 10 yards for that matter. Birdshot might be somewhat effective at boxing ring distances, if you can convince the bad guys to stay close enough...
……and because birdshot has worked in a few isolated instances does not prove it’s reliability. 00 buck and slugs are proven performers.
Folks have been killed with sharpened spoons, but don’t see anyone recommending those for self-defense.