Some very sensible comments have made this thread restore a little of my faith in musiciankind. I did a few years stint as live engineer, starting out with a couple of years in the studio, then spending alot of time shadowing accomplished live engineers for free whilst being an extra roadie, mic placement tweaker and general cable rat. Worked my way up through theatre work to meeting more and more arsey rock and roll gits who's MO seemed to be at odds with anything and everything I needed to do. Unsurprisingly these gigs more often seemed to be the ones where I was working under the most pressure (time/equipment/quality of gear) and wondering what, if at all, I was going to get paid. To be treated as some sort of incompetent, anti-musician by someone who doesn't understand what they're asking for, was one of the reasons I walked away from the profession, (but mainly the stress of its feast/famine financial situation). The bigger shows with more professional musicians understood that their responsibility was to play their instruments well and the engineers job was to make all the instruments sit together and sound right for the PA for the room.
If you don't have faith in your soundguy then you need to take steps to ensure that, the next time you play, that you do it with someone you can trust. That doesn't involve being aggressive or throwing a wobbly at your next engineer becaused you think they should be going about their business the way you think they should. You won't be doing yourself any favours.
/rant