Ideally, feminism is a subset of egalitarianism. In practice, the label "feminism," like many labels, ends up representing a whole host of varying views and agendas, and ends up picking up such huge amounts of semantical and ideological baggage, that it eventually becomes unproductive in its role as an effective label.
For the same reason, I don't generally refer to myself as an "atheist" in real life, since that is another label that is so loaded with baggage and differing interpretations as to be an ineffective label. Besides, "rationalist" is a more accurate and inclusive label for what I am, just like "egalitarian."
I'm not sure how "egalitarian" has become a dirty word. I can only chalk it up to people's ignorance of its meaning.