Who said “ flat freq response “ is the best?

There are a few subjects being discussed here: 
Flat response from Equipment and speakers
Flat In room response. 
If you think about it,  when the recording is done,  are they done in perfect rooms?  Carnegie Hall,  Studios, Restaurants, Church's.  Every recording will reflect the room that it was recorded in,  then our room has an effect again on what we hear.  The only way to hear the recording as it was done is with a flat room.  Ideally, all recordings would be done in a perfect anechoic chamber and our rooms would be the same, but its tough, shoving a symphony in a chamber. 
Next, for Equipment,  I do believe that it is important for our equipment to be producing a flat response.  That is the only way to faithfully reproduce the recording, assuming that we can have a perfect room.  I believe that it was @kalali that posed the question, would 2 different speakers with identical response curves sound the same in the same room.  I can answer that, I have built many speakers and have come EXTREMELY close in duplicating response curves, but I can tell you for a fact, not opinion that different driver materials sound different and on crossovers, even using the same slopes and same type of compensations or no compensation that crossover parts still sound differently from each other. 
Overall, my contention is Absolutely,  you need to come as close as possible to achieving a flat response curve on your electronics,  in your speakers and in your room.  If that is achieved.  It is then that you get as close as possible to creating that all allusive "Live" sound that we all work so hard to achieve.  Plus when things are acoustically flat, it does help hear so many other design presentation differences in amps, pre's, cables etc. 

Look around; you'll see that even ruler flat response bears little correlation between the perceived quality/acceptance of a speaker by the listener. 

I have handled enough speakers which deviated in some respects which others might consider unacceptable, yet they can be made to sound beguiling. People get hung up on the search for flat response, just as they� get hung up on the search for "The One," the perfect speaker. Imo, fairly fruitless efforts. 

I have heard plenty of systems which were purportedly "dialed in" to be flat response. Meh; they were pretty "flat" all right. 

To this point, no one has mentioned phase.

Minimum phase error trumps small deviations in frequency response in contribution to a realistic and non fatiguing presentation six ways to Sunday.

It is a great failing of the audio press that phase has been largely ignored for the half century since Richard Heyser's seminal work.

@ieales : 

The market has just not responded that well to it. While Vandersteen and Thiel have ardent followers they also have not dominated the high end speaker market. Neither have single driver designs. 

Best,

E