Most people I know take it because of their hormones but some take it as birth control and some just because they can't be bothered to have a period. Personally I have never taken oral contraceptives for the exact reason you state- I don't trust medications that aren't 100% necessary to be good for my body. When I joined my local surgery I just went in for an initial check up and the doctor tried to pressure me into getting a contraceptive implant, which I refused. She then tried to sell it to me on the basis that I'd have less periods and I told her that as it was natural and healthy for a woman my age to have them, I couldn't understand her reasoning. Finally she started on with the whole 'what if you get pregnant' spiel. Apparently she had never heard of condoms.
At the end of the day it's personal choice and some women need them for health reasons but I do think healthy women should look at other methods of contraception before jumping straight into taking the pill.