Everybody is entitled to their own opinion, but the idea of warning shots is totally foolish from my perspective. If you're ever in the situation where you have to draw your pistol in defense, the last thing you want to do is waste time making noise with warning shots.
If you worry about not being able to hit the aggressor without doing harm to bystanders, I would recommend more range time to hone your skills. Practice until you think you're really a great shot…then go and practice some more. You should never have to worry about misplaced shots, if you do you might re-think carrying a gun.