Feminism gets a pretty bad rap in general. There is this hideous stereotype of the mad, hairy, bra-burning lesbian for starters. But something else feminists get accused of is man-hating and "emasculation".
The man-hating thing is partly a myth constructed in order to foster distaste for feminism and to introduce the idea that feminism is actually inherently sexist. It's also partly the fault of women who go around saying things like, "All men are bastards," which frankly is usually because they only go out with bastards. It has extremely little if anything to do with feminists themselves.
Emasculation however does have a lot to do with feminism. Masculinity and femininity are cultural concepts that have little to do with gender. They have been constructed by a patriarchal society to exaggerate massively the small differences between men and women (men are generally more aggressive and women are generally more nurturing, and that's about it - and we can blame our hormones for those trends, not our brains) and to perpetuate a culture in which men rule the roost whilst women make the tea. The pressure to fit into these stereotypes and the male dominance inherent in them is something that feminists generally are not too happy about.
However, I don't think men should be emasculated any more than I think women should be de-feminised. Everybody should have the right to be who they want to be, within reason. I feel more feminine when I wear make up and pretty clothes and remove my body hair. This might be because I have been indoctrinated by the patriarchy to define my femininity in such a trite manner, but it's harmless and it makes me feel good about myself. Likewise, I don't begrudge a man anything that makes him feel more masculine, just as long as it doesn't involve him being a complete shit.
If a man's definition of masculinity involves raping, beating or lacking respect for women, seeing women as second class citizens, feeling superior to someone because he has a penis and they don't, refusing to do housework or valuing women solely for their fuckability, then I am only too happy to emasculate him. This "you're just trying to emasculate men" attitude is often used as an excuse for the perpetuation of misogyny by equating masculinity with scurrilous behaviour and attitudes. All feminism seeks to break down is misogyny, and therefore the only way a person could believe that feminists hate men is if their definition of masculinity is entirely tied up in the idea of all men being total gobshites.
Feminists hate misogyny
Masculinity = misogyny
Feminism = emasculation
Feminists hate men
If a man feels that his God-given right as a male is to earn more than female colleagues, get away with rape, visit dodgy brothels and value women only according to their sexual availability, then of course feminism is going to make him feel emasculated. Much as I try to avoid making sweeping statements about feminists in general, I think it's fair to say that none of us want to chop anyone's balls off. If you feel castrated by the thought of equality, you need to reassess your definition of masculinity.
I think that masculinity should be about self-identifying as male. Beyond that, there's not much to say. In terms of relations between the sexes, it should be about using one's greater size and strength for protection rather than dominance. It should be about being confident enough to be glad that women aren't stuck in the kitchen. It should be about valuing women as human beings even if you don't want to pork them.
Basically, be nice and we won't emasculate you :)