My clever wife pointed out that CBS has a long tradition of chickening out in the face of potential controversy.
In October 1968 CBS executives began to prescreen all of Smothers Brothers their [sic] programs. After several tumultuous seasons, the program was canceled (the Smothers Brothers called it being "Fired") and left the air in June of 1969. The CBS network justified their cancellation by referring to network policy that "Prohibits appeals for active support of any cause" (even if it was "peace").
This brings to mind a few more thoughts on CBS's refusal to air an ad by the United Church of Christ that touts the church's policy of tolerance. The Smothers Brothers case demonstrates that CBS has a long standing policy of avoiding controversy, though it is important to draw a distinction between controversy in programming (which clearly indicates some level of approval by the network) and controversy from advertisers (who are not under the editorial control of the network). The Smothers Brothers case is also interesting in that it came only a little more than a year after Walter Cronkite's famous 1968 report on the Viet Nam War during which he reported that the war was stalemated and advocated beginning negotiations with the North. CBS likes to take credit for the personal bravery of Cronkite and others in their news division, credit to which the network as a whole certainly is not entitled.