Does iPhone need a case?

I checked out videos with people trying to scratch the screen with knives, keys and such and they couldn't. I'm mainly worried about the touch screen but also the case. I don't want any scratches on my screen, so does iPhone need a case to prevent scratches?

I will get one if I have to, but I don't exactly want one because I don't want anything covering up the gorgeous look of the iPhone. Plus I can't exactly find a case that looks good.

Thanks