I think people say that because its the textbook answer and they think its the right thing to say. In a way they're correct, and in another way trip20 is right, ya kinda gotta be there to know if it'd help or not. Sometimes it might be the right thing to do (draw without immediately firing).
I'd rather draw without firing than the reverse. Who wants to kill? It might escalate the situation or it might just strtegically defuse it too! One time when I was a security guard and got (attacked) by some guy I basically beat the crap out of him with a PR-24 and got on the radio to have the local po po come over and take a report...he cussed at me and went for his pocket. I dropped the radio and drew my pistol, but on a 45 degt angle without pointing it at him. It turned out that he was going for his car keys instead of an AMT Backup because he didn't want to be arrested. I'm glad I didn't shoot him! Should I have waited to see what he pulled out before I drew? I think not. It could've been a pistol.
It's all situational ethics. You gotta be there to know. I'da stood a better chance, having mine drawn already if he did pull a pistol. As it turned out, no harm no foul. You just need to be able to articulate good reasons for your actions for the aftermath. No easy answer here but do what ya gotta do without crossing the wrong line.
A couple other times I put my hand on it without drawing and defused the situation. BG's know that going for the gun movement and generally stop.