Like John said, on the Big Boy level it's the labels and the artists duking it out assininely in the RMS wars.
On our level where we're mostly dealing with clients with names who have not yet appears on a Billboard chart, it's mostly a bunch of uneducated ears interfaced with un-informed minds who simply believe "louder is better" and haven't thought about it any beyond that. I think we have the obligation to work out at least a gentleman's undertanding if not a working agreement just where each of the nominal producer responsibilities lie in such situations. How much of our ears, our expertise and our experience are they hiring? How much trust are they going to put into our technical and creative decisions?
If the bandleader or manager insists on their own full creative control, including decisions on volume, and that agreement is understood from the get go, then we just have to grin and bare it. (BTW, if we do det permission to use their stuff in our portfolio, that doesn't mean we can't keep a pre-smashed version of the mix for ourselves to use in that portfolio

.)
However, if it's a band or performer with whom a short conversation reveals that they are hiring us as an engineer and not just a prosthetic arm, the opportunity is open to help them find an understanding that one of the main reasons they are hiring us is for our ears, and ask them to place a little benefit of doubt at least that our ears are telling us something their ears are not when it comes to volume.
Give them two mixes, one smashed and one not, and discuss with them why one sounds better then the other. Give them a brief education. If we've built their trust, they might actually listen to us. If not, and they still want the inferior one, so be it. Take their money and move on.
G.