Not at all. The facts that McDonald's serves fast food, and that I sometimes go there, doesn't mean it's the only thing I eat.

Aside from the possibility that some of us may knowingly visit both FT and porn sites, one sometimes gets there by accident. A high-school senior, then in my household, once went to whitehouse.com (NSFW!) in the school library instead of whitehouse.gov. While this incident didn't result in any damage to the computer, that sort of thing happens for any number of reasons. One should be aware of all the risks besides going blind.