And why we have Wikipedia:
Despite its being an apparently trivial topic, some people hold strong opinions on the matter. Advice columnist Ann Landers said that the subject was the most controversial issue in her column's history. Defenders of either position cite advantages ranging from aesthetics, hospitality, and cleanliness to paper conservation, the ease of detaching individual squares, and compatibility with a recreational vehicle or a cat. Celebrities and experts are found on both sides. Some writers have proposed connections to age, sex, or political philosophy; and survey evidence has shown a correlation with socioeconomic status.
Solutions range from compromise, to using separate dispensers or separate bathrooms entirely, or simply ignoring the issue altogether. One man advocates a plan under which his country will standardize on a single forced orientation, and at least one inventor hopes to popularize a new kind of toilet roll holder which swivels from one orientation to the other.
Once you've had quite enough of this sort of thing, be sure to scroll down to Similar Controversies.