I do agree with what you're saying, but what I'm trying to explain (poorly) is when you get an inexperienced person leaving 3 or 4 channels right up in the red constantly (for what ever processing reason) for the whole duration of the track and instead of correcting the problem they pull the master fader down just because they don't want the master to clip, then start fiddling around with the other faders only to spend wasted time trying to get things to sound right. It just isn't a great way to go about things. Or worse yet, not even touching the master and sticking a limiter on there to stop it clipping and to make it louder, that's when the real mess starts.
As you said, if the channels are all not clipping at unity, but causing the master to jump then, by all means pull it down a little on the master, or just mix at lower volumes and crank the speakers.
I agree, there really is no justification for lighting up the peak indicators on mixer channels. If you're having to push the channels that far, you've got issues with your gain staging that need to be addressed. That's by I like using 0dB as my reference for the mix ceiling: it's not unusual when browsing through samples for layers for, say, percussion and to roughly "mix" (in very loose terms) the layers so that they perceptibly sit in the mix, but looking at the meters you can see it going either over unity or close to 0dB (my ceiling). This instantly signals to me that I need to clear up the dynamics of that sound so that I can push it far lower in the mix whilst having it perceptibly at the same volume as before. But of course, this is all personal work flow stuff so as long as the bad practices we have discussed are avoided, any perspective is legitimate of it works for you.