44man, if you can shoot the big guns and are confident with them then by all means do so. I won't disparage anyone's choice of protection as long as they return the favor. I will agree with you that better than nothing is about the nicest thing you can say about most of the craptastic factory ammo available for the .25 Auto, .38 S&W, and even many .38 Special varieties. These are all watered down big time so they won't blow up granny's lemon squeezer or questionable pre-'68 import.
Now, good reloads or factory ammo of known quality and performance can significantly change the equation. No, it doesn't transform the mousegun into a manstopper just as a big bore doesn't guarantee one shot stops 100% of the time. However good ammo with consistent velocity that is up where it is supposed to be will have likely have enough penetration to kill or seriously injure the bad guy if the defender can place the round where it needs to go. Which, he/she will have a better chance of doing as they are confident and practiced with their "small" gun, instead of one that is beyond their ability.