If you believe jw doctrine and "being appointed by holy spirit" of the CO and yourself - and I suppose most elders sat in a meeting with a CO do - then that puts the brakes on them speaking out. If a CO rides roughshod over a body of elders in those circumstances then anyone speaking out will be quickly crushed by the CO's "authority" and the elders compliance with "Jehovah's arrangement".
If you don't beleive all the above rubbish and you're still on the body then Jeff T's "middle manager" scenario in his post above is absolutely spot on. I know this from being in exactly that position. When I resigned as an elder in around 2004 it was due to a strong difference of opinion with the CO and the other elders simply did a lot of handwringing and basically said they would keep their heads down for a couple of years and wait for the CO to "move on." When he left they actually asked me to go back on the body but I was free and clear and still well thought of in the congregation so declined.
Back then I still beleived (gullible fool that I was) enough that if the Holy Spirit was really involved then that CO would be removed at the end of his three year slot (which was due up in 2006) because his behaviour - arrogance, going overtime bigtime, shouting on the platform - was being whispered about in all the congregations in our circuit and being brought up with the DO and the branch. But no ... He went on to another circuit and did exactly the same and has just been sent to another one where he is up to his old tricks again. (Ecclesiastes 8 v 11 )
So for me, standing up to the CO was the best thing I ever did - I resigned from being an elder on the service committee and had no more group to look after or regional build responsibilities - and just sat back. But if anyone wants action taken against a CO they'd better have big gun back up and a cast iron case of almost judicial proportions.