Updated 3:08 p.m. ET

Herman Cain insisted Sunday that his now-viral campaign video featuring chief of staff Mark Block dragging on a cigarette was not meant to send a message that smoking is cool.

The GOP presidential candidate, appearing on CBS' Face the Nation, was chided by host Bob Schieffer for the Web video, which now has been viewed about 1.3 million times on YouTube.

"One of the themes within this campaign is let Herman be Herman," Cain said. "Mark Block is a smoker and we say let Mark be Mark. Let people be people."

But Schieffer, who battled bladder cancer, pushed back on Cain's assertion that there was no subliminal message behind the Web video. The TV journalist called on the former pizza executive -- who is also a cancer survivor -- to come out and say he's not endorsing smoking. Schieffer has blamed his cancer on smoking.

"Young people of America, all people, do not smoke. It is hazardous and it's dangerous to your health. Don't smoke," Cain said. At Schieffer's behest he added: "It is not a cool thing to do."

Cain said he won't take down the video from his campaign's YouTube channel, noting that even if he did it would still be available elsewhere on the Internet.

The candidate estimated "about 30%" of the reaction to the ad was similar to Schieffer's objections.

On other topics, Cain vowed to be more careful about his public statements on topics such as immigration, which have gotten him in trouble in recent weeks. Cain recently said he was joking when he suggested that an electrified fence and a moat could be used to keep illegal immigrants out of the United States.

"As I get more attention I will tone down the humor," Cain said on CBS, adding that would change if he gets elected president because he still believes "America needs to get a sense of humor."