One can be an activist in support of a cause without being a person who defines that cause. When we're talking about a cause that relates to oppressed people speaking out against oppression, and overthrowing it, it's really important that the oppressed group has the defining role in that cause. As a heterosexual woman, I will never experience homophobia directed against me in the way that a gay person experiences it-- so therefore, I cannot say that "a" is homophobic" while "b" is not-- it's just not my place. I can be an activist in support of gay rights, but I will never be a Lesbian activist, no matter how I might empathise.

In terms of feminism, you will never experience misogyny in the way that women experience it. Certainly, there are things you can contribute to dialogues about women and discrimination-- you can raise awareness about types of misogyny you have witnessed, you can look at how this affects gender roles more broadly-- but you can't be the person defining where misogyny occurs and where it does not, simply because you're not the person who will be on the receiving end of it. To many women, to be a feminist means to have a defining role within the women's rights movement (a movement in which both women and men participate)-- and as such, a male feminist is someone claiming a defining role in a movement that he cannot define.

There are a couple of other reasons that women might be sceptical of men calling themselves feminists-- I am going to say these things, not to accuse you of these behaviours, but simply to explain the behaviours that many feminists have encountered.

The first of these is what I'll call the "I deserve a cookie" attitude. This can be found in many movements that are aimed at ending oppression-- a member of the non-oppressed group will make themselves out to be a Wonderful Amazing Person Deserving of Many Accolades because they support the movement. Implicit in this attitude is that the oppressed group should spend a significant amount of time applauding and baking cookies for non-oppressed supporters for simply being there. However, supporting movements that involve simply treating other human beings with the dignity and respect due to a human being is not a Great and Wonderful thing to do-- it's basic decency, and no-one gets a cookie for it.

Another reason that many women are wary of men calling themselves feminists is the "I am a feminist, therefore nothing I do is sexist-- now show us your tits!" attitude. This comes back to what I was saying before about defining roles-- the label of feminist is used to define actions as sexist or not-sexist, without actually examining why those actions might be sexist or misogynist, and the effects of those actions on actual women.

Regarding your experience on the feminist message board: Of course, I don't know exactly why you were banned, but usually when this sort of thing happens, it's because you're not fostering a positive community environment in some way. Now, I've never been banned from a message board, but I have been made to feel unwelcome on feminist boards. I was bitter about this for a long time, and it even turned me off feminism for a while. However, the problem, I later realised, was not with the people on the boards, but with me. I went onto those boards thinking that I had all the answers about feminism, and that if anyone disagreed with me I was going to "enlighten" them (because surely, none of these women had thought through all of these issues before!) So instead of taking some time to listen to why people might hold a different opinion to my own, I blasted in there, and disrupted discussions, and basically made a right fool of myself (although at the time I thought I was some sort of powerful and wonderful voice of dissent). Since I've made more effort to listen before talking, I have not found nearly so many unwelcoming attitudes. I still disagree with many other feminists on many points (and indeed, I still hold many-- but not all-- of the opinions that I expressed in my earlier forays into feminist message boards), but taking the time to listen and address disagreements respectfully has helped a lot. In your case, because you don't play a defining role in feminism, listening is twice as important. Sometimes you may hear things that you disagree with initially, and I'd recommend that before responding, you take a long hard look at (a) WHY that person holds a view that you disagree with, and (b) why you disagree with them. Always, always, listen-- and listen hard-- before you speak, or before you dismiss someone as unrighteously bitter.