As the patient, you can choose to not have sedation if that is what you want, even if it is the doctor's preference. People have all sorts of reasons from difficulty obtaining a ride to not wanting to feel "rummy" all day.
My GI always takes biopsies and I never have had sedation except for a full blown colonoscopy, and that was last done 20 years ago. Biopsies do not hurt, since there are no pain sensor nerves in the bowel wall. The discomfort you feel is from the distention from the air they pump you up with.
So, bottom line; if you do not want sedation, just say you don't want it. My GI says that many of the other doctors at Kaiser even prefer to have their routine screening colonoscopy without sedation, so they can return to work afterwards. Now, THAT'S a dedicated doctor!
Jan