I wouldn't want to see them trade Ben either, but to play devils advocate:
His cap hit could help sign others. He is not getting any younger. With his play style, he is one hit away from the disabled list at any time. Yeah I know, this can be said of anyone, but as I said, with his style, the odds are greater/riskier. Yes, no proven QB behind him. Well, they need to aquire another QB eventually anyways. Why not try to get something for him while they can? Surely they could. No, not many teams would be willing to take his salary on, but there will ALWAYS be teams that would, ala Oakland and the Redskins. Not saying they would, but they are the types of teams/management, that would. Just using them as an example based on their history to nix anyone worried that other teams might worry about the $. The NFL is changing on the offensive side. Teams who have smart pocket passers are thriving. Does anyone here consider Ben a smart pocket passer type?  Yes, his style of play extends plays. But it can be a curse, too, as anyone with half a football brain who watches him can attest to.
All that said, as stated here, I don't wanna see him go.  But if by chance he does, I don't think it would be the end of the world.  It certainly can't get any worse for the Steelers.  His prime is almost gone.  And during that time, the Steelers will NOT be contenders anyways.