Genuine feminists are not men-haters; they are about female empowerment, and opposition to any type of discrimination, or institutions that foster such discrimination, along gender lines, or any other type of lines, plain and simple. Their beef is with these institutions, and the concept of discrimination itself, not men.
And not all lesbians are man-haters, of course. Many have no problem being friends with men and working alongside them as equals; they are simply not attracted to them romantically. They likewise have no problem with women who are naturally straight and do desire romance with men. They accept the existence of heterosexuality, as well as bisexuality, and they simply want acceptance for woman/woman love, not its dominance as some sort of morally superior preference for all women to have.
The 'femi-nazis' (as they have been coined by radio mouthpiece right-wingers like Rush Limbaugh) are, as far as I'm concerned, not true feminists, but reverse hate-mongers, who dislike all heterosexuality, dislike anything to do with men, and do not oppose tyrannical, prejudice-fostering institutions but simply the fact that it's men who currently dominate those institutions instead of women. If such women dominated those institutions themselves, the world would not be free from a single problem we have today, even if you were a woman, and most importantly, a lesbian. Their reactionary ideology proves that women are potentially just as bad as men when in control of institutions deriving from a class-divided society, and that their agenda is not about justice, but pure vengeance.