Nancy I don't think it is about "judging as to who makes the grade", although I can sometimes understand why people might perceive it that way.
I think what happens a lot is that a woman who considers herself a feminist, because she believes in female/male equality, can be challenged on a certain view that, when analysed or challenged, is not actually compatible with the tenets of feminism.
For example, I'm a feminist (and quite a radical one). However I changed my name when I got married. I have reasons why I did this and I could try to argue that they are feminist reasons because I am feminist and a woman. When analysed, it is likely, that my arguments would be shown not to be compatible with feminist tenets. Feminists pointing this out to me are not being judgemental - they are protecting feminism from being watered down from a political moment with beliefs, analysis and aims, to a wishy washy, anything goes, nonpolitical hotch potch.
I see woman after woman take the hump because they have expressed a view that is a bit short on feminists analysis and have been challenged on that. Feminism is pretty black and white really - of course there are different viewpoints within the movement, but the fundamentals are pretty clear.
The 'trap' with feminism is that, by definition, it challenges actions and views that are commonly thought to be right, normal, fair and natural. It is difficult to get your head around feminism sometimes and break away from patriarchal thinking.