Communism and Capitalism have huge followings world-wide and are very well-established and documented forms of government. Libertarian is a descriptive word like Liberal or Conservative which describes a wide field of political thought and ideological leaning based on core principals. Like "Capitalist", "Communist", "Liberal", or "Conservative", "Libertarian" describes ideals surrounding the structure and application of government. I don't know about the Free-Trade tag, but I suspect it has more to do with Role-Playing than actual politics.
Feminism is a specific movement, more similar to a party affiliation or a specific religion than a general governmental or economic structure or system of laws. While there may be many different views held by feminists, that does not make feminism a broad ideology. Feminism cannot be treated as having general principals like Egalitarianism can: Egalitarianism holds that all people are equal; Feminism only holds that men and women are equal. In other words, individual political ideologies may hold differing degrees of Egalitarianism, but the question of Feminist or Not Feminist is binary.
The point is, Feminism does not describe a form of government, economic structure, or general political leaning. It is extraordinarily specific and its addition to the tag cloud would justify the addition of many other things that would bloat it.
(I would also like to point out that if you are advocating to add "Feminist" to the tag cloud, you must also support the addition of "Masculist", as Masculism is the egalitarian opposite of Feminism. I don't want to see either, but if "Feminist" is added to the cloud there is every reason to add "Masculist" as well. Just food for thought.)