Doug,
You've hit on a subject that has long been a pet peeve of mine. There was some discussion around this issue at the (very excellant) grounding seminar done by Bill Whitlock at 695 recently.
You certainly did the right thing, and the fact that your mixer was enough of an idiot to ridicule you for standing up for you're safety says a lot about the ignorance exhibited by many crews working within the industry are when it comes to basic electricity.
I still don't understand why this isn't dealt with as part of the "Safety Pass" classes. It should be a basic requirement for at least the Mixer, but ideally the full sound crew, as well as the video assist crew.
I have witnessed more than a few occassions where a camera operator was nearly knocked off the dolly because the camera body was hot, due to the fact that it takes it's ground from the video assist cart. Before the time that I completely isolated our cart from video assist, I once had a 65 volt difference in potential from the video cable send to us, which needless to say didn't sit well when it was connected to our cart!
These days, I carry a ground rod and cable that we can ground our cart with, and if we take power from the genny, I have a jumper that we can remove to isolate our ground from the generator ground. All you have to do is think about the amount of leakage that can get into the distro ground from various sources, and you will think twice about ever using the genny ground at all.
I am still at a loss to understand the thinking regarding not grounding the production gennies; especially in wet weather situations, when all kinds of leakage occurs from the power distro and lamps. I have had this discussion with a lot of genny operators and electricians, and it amazes me that many of them still just don't get it. When we have no choice but to take power from the genny, I always check to make sure that it's grounded. (I actually walk over to check it, as I've been lied to about it in the past). Although a couple of guys have complained initially, after I ask them to put one hand on their ground conductor, and their other hand to a convenient earth ground (sign post, fence post, etc), I see their attitude begin to change.
There are plenty of ways to get a healthy dose of electricity on a set, which should be obvious to anyone who takes a few minutes to think out the grounding paths between camera, sound and video on a typical set (at least if a hard wire connection exists between them).
This is one area where a lot of ignorance still exists, and I don't see it getting better any time soon. In the meantime, follow your best instincts.
Scott D. Smith C.A.S.