I have to disagree.
1.) there is no need for a "sell all" button. if you need no more gold, then why would you care about easier selling of stuff? that would just give you more gold lol. you can just simply let them sit there till they disappear.
2.) it would in fact be counterproductive/damaging to have a "sell all" button. even the "reclaim all" button is such a pain, people have been hitting it accidentally so often that it had to be removed with a script. a "sell all" button is even worse.