How so? If a director directs an actor to say a line seceral different, and he ultimately chooses one take to be in the final cut, how can you blame the actor?
By virtue of the actor having said the bad version of the line. Even if the director says "I want you to say it this way," and the actor does so with a bad result, the actor is still responsible not being able to give the director what he wants without having it suck. Please note that I pointed out specifically that the director shares responsibility. I am not saying "ZOMG, IT ALL TEH ACTOR FAULT HE SUCK." I am saying the actor, except in extreme cases (as with Clooney), always shares the responsibility for the quality of his performance. Accordingly, saying "you can't really blame the actor" is simply not true.
Obviously, the actor does play the role and speak the lines, but I'd put more blame on the director for directing that actor and choosing a questionable take.
In my opinion, part of a director's job is to get convincing performances from his actors. Yes, it's an actor's job to be good at what he does, but when the director ultimately makes the decisions about everything, how can the blame rest with the actor?
So are there no bad performances, just bad directors? Part of the actor's job is to give a convincing performance--and that includes convincing the director. If that job is done, you've got less chance of a director saying "Nope, we're gonna do it my way instead," because the performance will have convinced him.
It's simply not as cut and dry as saying "Oh, the director made the final call." Equilibrium is watchable because Christian Bale's acting surpassed the quality of the directing (and the terrible scripting, derivative trashiness, and overall suckitude of every other thing in that entire movie, besides the action), so that not even crappy decisions on the part of the director could ruin his performance. On the other end of the spectrum, if you had given the Equilibrium script to Tom Welling, the performance would have sucked because Tom Welling sucks.
The director is always responsible, naturally, for choosing the actors and directing their performances. But, likewise, the actor is just as responsible for contributing a crappy performance, or being unable to reconcile the director's goals with a quality performance.