Facebook invites participants to disclose their political views. Different national contexts are shaped by different political forces. The Facebook selection represents a US view of those forces.
Take 'liberal' for example. As expected, most folks in the library community self-disclose as 'liberal' or 'very liberal'. However, 'liberal' is a rather complex word. See for example the disambiguation page on Wikipedia. Here is some text from the entry on Modern American Liberalism:
Today the word "liberalism" is used differently in different countries. (See Liberalism worldwide) One of the greatest contrasts is between the usage in the United States and usage in Continental Europe. According to Arthur Schlesinger, Jr. (writing in 1962), "Liberalism in the American usage has little in common with the word as used in the politics of any European country, save possibly Britain." [Modern liberalism in the United States - Wikipedia, the free encyclopedia]
And I read in New Keywords:
The term subsequently traveled to other European countries and later to the United States, in each of which it acquired somewhat different meanings and represented different policies. In France, "liberalism" retains a strong connotation of moral anarchy and rebelliousness; in Britain it stresses individual liberty and limited government; and in the United States, where it did not become current until well into the C20, it conveys a strong and active government, concentration of power in the federal government, and support for affirmative action. Despite these differences between different national traditions, which have persuaded many writers to talk of liberalisms in the plural (J. Gray, 1989), certain core ideas remain common to them all. [New keywords, p. 199]
It may be that Facebook will assist the general trend towards adoption of US words and senses, although this is a complex area. So, some of the people in the UK who self-describe as 'liberal' might more naturally self-describe as 'social democrat' or 'left' and favor more collectivist approaches (welfare state, publicly funded education, etc.) than 'liberal' might in other contexts suggest.
The use of 'libertarian' may be symptomatic of this mismatch between Facebook's US context and the situation elsewhere. I am sure that some of the people who self-describe as 'libertarian' outside of the US are seeing 'libertarian' as an expression of left/liberal views, and may not recognize the ways in which libertarianism is located within the forcefield of US political positions.
All that said, I reckon 'apathetic' is probably a category with a globally agreed sense ;-)