If its the polyp removal, I can certainly see how that could lead to problems. But you're a little stuck: even if you use another technique to do the scan, you still have to remove any polyps you find, don't you?
I'm not sure what the botches are here. In the sigmoidoscopy they took out a couple of polyps, in the colonoscopy (more recently than the sigmoidoscopy) they just did a cancer check-up given family history.
I wish those articles discusses the "botches", I'd like to know since from my understanding these are pretty safe procedures
Based on your concern, the question is whether 'botched' procedures are more or less of a risk (both in incidence and consequence) than non-screening.
Read the safety statistics and let it override the anecdotes. Colon cancer is easy to prevent and a horrible way to die.
The complication rate for colonoscopy is about 3 in 1000, and that is skewed towards people who have polyps, which in and of themselves could be dangerous if not removed.
So it's always a risk tradeoff. You can skip the procedure and risk the effects of the disease it's supposed to detect instead. But if you do the math, you're statistically better off doing the procedure.