Every once in a while, when discussing racism/sexism/homophobia/ableism/generalized prejudice with people, you'll see the classic line, "But I can't be prejudiced! My friends/family/significant others have been members of this minority and we get along great!" Occasionally, you'll see it pushed beyond "we get along" to "they agree with me", but the general thrust is that if you can find a member of the group who you're accused of prejudice against who shares your views and is willing to say nice things about you, then clearly you can't really be prejudiced against that group. This has become known as "using them as a shield".
(Every once in a while, by the way, you'll find someone engaging in the cargo cult debating practice of accusing people who argue against racism of using minorities as a shield by ignoring the members of the minority who agree with the racists. GamerGate loved this tactic, frequently making up fictional members of minority groups who agreed with them when the actual minorities who agreed with them proved to be rather thin on the ground.)
Often, the people who use women and minorities as a shield get very upset about being accused of using women and minorities as a shield, because they think it implies that not only are they prejudiced, which they clearly can't be because they have friends who are women and minorities, but that those relationships they value are false or only there to defend them from criticism. If you're one of those people, let me try now to explain to you, in what will hopefully be calm and friendly terms, why you're wrong--and not just wrong, but wrong in a way that is in and of itself prejudiced.
You're wrong because you're thinking about "prejudice" in its colloquial, everyday sense--hatred for minorities, or the belief in one's racial superiority. But really, prejudice is more than just that--literally, it means to pre-judge, to ascribe traits to an individual based not on the direct evidence of their personality or behavior, but because of the traits you imagine members of that group to have. It usually means negative traits, but it doesn't have to--deciding that all black people are good at basketball isn't hateful, because telling someone they're good at something is usually a compliment, but it is an act of prejudice, because it's not always true and it's making an assumption about someone based on race.
It's important to note that this prejudice works both ways. If you meet one woman who gets upset easily the week before their period, and you generalize that claim to "all women get really emotional right before their menstrual cycle", you are engaging in an act of prejudice even if you can point to specific instances that support your beliefs. Because you are judging every woman, in advance, based on the actions of one woman. (And again, this holds true even if the act of prejudice is behaviorally neutral. Liking watermelon is a behaviorally neutral act. Insisting that the stereotype of black people liking watermelon is true because your co-worker was black and he loved watermelon is racist.)
So if your defense against a claim of prejudice is to cite an individual who's a member of that group and point out that they agree with you, you're engaging in an act of prejudice right there. You are taking the opinions of one person you know who supports your position (or who you believe to support your position--I could probably write a whole additional column on the ways that "not arguing with me openly and continually" is conflated with "agreeing with me" by bigots) and generalizing them out to, "All people of this group support me, and so I can't be racist because I have so much support from minorities." The very defense of bringing in a minority as a shield is, in and of itself, a clear sign that you don't really get what your problem is.
That's why the "#notyourshield" argument that GamerGate made comes from a false place and inevitably fails. It assumes that people arguing against prejudice are doing the same thing they're doing--finding women who agree with their viewpoint and holding them up as examples--and that if they can find enough counter-examples, then they can "prove" that they're not sexist. But it doesn't work that way because the definition of "sexism" isn't simply "doing something a woman dislikes", it's ascribing traits to all women based on the actions of an individual woman, or ascribing traits to an individual woman based on your beliefs about women as a group. When you do that, you're being sexist whether or not you can find one or more women who say you're not.
To give another, purely hypothetical example, let's imagine a person named B. Torgersen--no, wait. That's too obvious. Let's call him Brad T. Let's say that Brad T. says that women and minorities "benefit from Affirmative Action" when they win an award--purely for hypothetical purposes, we'll pick the Hugo Awards, but it could be any major science-fiction writing awards. This is an act of prejudice--it is a direct implication that women and minorities are not as talented as white men, and that they need to have factors other than the quality of their work taken into account in order for them to win the award.
Now, Brad T.' comment could be defended on the grounds that he's not talking about all women and minorities; he's just giving specific examples of women and minorities who did win despite other work being better on the merits. It's a pretty weak counter-argument, because it denies the possibility of bias on his part while insisting everyone else is subject to bias, but he could try to make it work. Perhaps he could cite examples of worthy works that were overlooked in favor of these supposed inferior stories.
Instead, our hypothetical Brad T. insists that he can't be racist or sexist, because he's married to a black woman. Note that this is, in and of itself, a prejudiced act on a number of levels. He's assuming that the only kind of prejudice possible is irrational hatred of women and minorities, rather than unthinking assumptions about them. He's assuming that his wife's emotional support of him as a person equates to support for his beliefs that women and minorities are not as talented as white men. And most importantly, he's assuming that if one black woman agrees with him, then all black women must agree with him. In trying to defend himself against prejudice, he has unwittingly exposed a whole host of further unexamined assumptions about race and gender, and demanded that they remain unexamined because to do otherwise implies that he doesn't really love his wife.
This is using a minority as a shield. It's not a hateful act--again, this isn't an implication that the relationship exists only as a defense against criticism--but it is an act of prejudice. Every single time. And if you find yourself in that position, of saying, "But all my friends are--" or "My family members are--" or "My loved ones are--" instead of engaging with an argument on the merits, stop. Take a step back. Calm down. And try to ask yourself why it is that you need your friends or family or loved ones to validate your opinions for you.