Is quitting smoking necessary for colon cleanse?

I have been smoking for 11 years, and I have tried to quit in the past, but was unsuccessful. Lately, I have been looking into colon cleansing and its benefits, and would like to try it. One of the recommendations was absolutely no smoking. I know smoking is bad, and I know that it seems pointless to even consider a cleanse if I’m gonna smoke. I was just wondering if smoking causes MORE damage or are they suggesting that it is just GENERALLY a bad thing to do?