I knew a couple people would respond to the backdrop thing.
I believe that the term you used was "backSTOP", NOT "backdrop". They mean different things.
As commonly understood, a "backdrop" is merely something in the background, as in a "backdrop" on a theater stage. This could be anything from a blanket on a clothesline to the clothesline by itself, to a crowd of bystanders.
A "backSTOP" on the other hand, is commonly understood to be something which STOPS or redirects a projectile, as in an inclined metal plate, a metal "snail shell" bullet trap, an earthen bank, or captive tire crumb into which bullets are fired, safely containing the projectile and any fragments thereof.
If I miss my intended target, it doesn't matter what kind of projectile I use. On the other hand, if I hit my intended target and it passes completely through that target, that makes a BIG difference. I cannot GUARANTEE that the .45 200gr. Hornady TAP JHPs, 9mm 147gr. Winchester White Box JHPs or .38 158gr. Federal LSWC-HPs that I carry in my handguns won't pass completely through an assailant and hit an innocent. It is beyond reason to deny that they LESSEN that possibility measureably.
As hard a I try, I can't think of a SINGLE plausible negative factor of using proper expanding self-defense ammunition that can even come close to outweighing the benefit of keeping my bullet(s) inside of an assailant.