This threak again...
There are lots of bad ones, and they don't stick around long. But there are usually some very good ones too. They know there stuff, and better still, they motivate the person to get into the gym. I've seen one in particular who carries a noticeble amount of flab (but can lead a high intensity aerobics class for 60 minutes that would probably kill me) but he's a terrific cheerleader and is especially good at motivating the older set who are in terrible shape. he keeps them coming in and I know some feel he's improved their quality of life.
Don't forget, for the majority (even those in shape), crossing the threshold into a gym (even just starting to put on running shoes and jog) is very daunting.
Unlike all the bro-scientologists online, most people are not into fitness, they don't see it as a hobby but instead as a "necessary evil" and are not interested in the discomfort that comes with getting fit.
If there is somebody out there that can help those people overcome that, cheers to them.
For the record, I'm not totally altruistic about this, I do gripe about bad trainers, dumb routines, and the noobs taking up space in my crowded gym too.
I find that when I let them get to me, it's a reminder that I am not paying enough atention on my workout and to get my head on straight.