I agree.  This is horrible.  This approach hasn't worked.  But let's get specific.

What's wrong with the idea that "you need to attack the first good pitch you see, because in the majors, pitchers will put you away if you go deep in the count"?

I can see several possibilities.  
a) ML pitchers aren't that much better than AAA pitchers at hitting their spots
b) The advice presumes the hitter cannot hit a breaking ball (usually the "out pitch")
c) The advice presumes the hitter cannot lay off pitches outside the zone with two strikes
d) The hitter is assumed to have a relatively small hitting zone in which he can really drive the ball, as opposed to going with the pitch
e) It ignores the fact that forcing the pitcher to throw more pitches, while making it harder for any one batter to succeed, makes it easier for other batters to succeed, and more likely force the other team to use their middle relievers
f) It ignores the possibility that by watching a few pitches, a batter will improve his ability to follow the pitcher's release point and timing, improving the batter's contact
g) It overvalues hits relative to walks
h) It represents, for a batter like Theriot, a departure from the pattern that has made him successful, just at the point where he is already dealing with other major changes
i) It fails to see that hitting a "hittable" pitch from a groundball pitcher is likely to result in an out (Zambrano would love it if everyone swung and hit a first-pitch sinker)
j) It sets up an obvious tendency for a pitcher to take advantage of, rather than forcing him to come up with a specific game plan for each hitter
k) It suggests hitters should focus on the quality of the pitch (reactive), rather than preparing to hit any pitch that land in a hitter's favored zone (proactive)
l) It is an approach to hitting that cannot be practiced in the cage or batting practice, thus likely has a long learning curve

Please add others or comment on which of these you think is the real reason the philosophy fails.

I am in my 40s.  While I retain many of the beliefs and habits learned from my parents, I have also changed major parts of my worldview and behavior.  These changes have almost NEVER come when confronted with the choice directly, or in public view.  Instead, at some quiet point of reflection, I realized that no longer believed X, but understood Y was a distinct possibility.  Or, in privacy, I tried something new, and found I liked it.  I'm not talking about developing new vices, just things like foods I never ate as a child, or political ideas.    

While Dusty has started talking more about OBA and being patient, I do not believe that he, Gene Clines, or Sonny Jackson will change their fundamental views of hitting "aggressiveness."  As a former hitting coach, Baker will also be incapable of leaving the coaching to someone else who has a different philosophy.  But a lot of us already think Dusty is gone at the end of the year.  My bigger concern is Jim Hendry.  His bosses do not understand how critical this issue is, but unless Hendry has been doing some serious thinking behind the scenes this year, I think he will have to be fired also for the Cubs' hitting philosophy to change.  

Mr. MacPhail, please change general managers.  

At any time during this interview did Theriot expressly say this is what he was told to do by his big league coaches or did he say he came to the conclusion about hitting the first decent pitch on his own? Or did that not get addressed at all?