That's like saying that we should never speak of how terribly wrong FDR was
when he put thousands of American citizens (Japanese-Americans) into internment camps at the onset of WWII. After all, FDR was a great President, so we shouldn't criticize him, right? The fact of the matter is that when FDR put those Americans into those camps, and when most of America cheered him for doing so, it was a tragedy for our nation precisely because we failed to live up to our values and our ideals.
And official, US gov't sanctioned torture is another shameful example of failing to live up to our ideals.
We draw attention to it because we must never let it happen again - we're better than that.