Do all polyps need to be removed in colonoscopy to avoid colon cancer?

Yes, if possible: When you have a colonoscopy and polyps are found- as much as possible, all those polyps- especially the ones that are quite large and look suspicious- would need to be removed ( if possible) to prevent the risk to develop into something more serious- like cancer.

Yes: Not all polyps are pre-canerous, most are. The determination of whether the polyp is precancerous or not usually requires examination by a pathologist and that necessitates removal. There is no good reason to not remove a polyp detected on colonscopy. All most all colon cancers start in polyps, therefore it is necessary to remove polyps to prevent colon cancer.

Generally yes.: Most but not all polyps are precancerous and need to be removed.