Why it would be okay to out Rick Santorum
Mark Kleiman and Ted Barlow are categorically opposed to outing. They argue that it is wrong publicize the sex lives of politicians, even politicians who slander gays and assail gay rights in public while indulging in private gay sex. There are many good arguments against outing. It violates personal privacy, it harms innocents, it spreads inflammatory and irrelevant information. In some cases, the threat of outing comes uncomfortably close to blackmail.
That said, outing may be defensible under certain extraordinary circumstances. For example, I would feel entitled (maybe even obliged) to out Rick Santorum if I were to obtain incontrovertible evidence that Senator Santorum was indulging in infidelity, homosexuality, polygamy, bestiality, or any of the litany of sexual practices he condemns.
However, outing is only justified under the following conditions.
1. The target must be an elected official. It is not acceptable to target members of an official's staff, his family, or non-elected officials. Elected officials don't have the same right to privacy as private citizens. We are already comfortable discussing many intimate details of politicians' lives including their parenting skills, their drug use, and their private religious beliefs. These discussions aren't usually considered immoral. (Maybe it's immoral to make specious arguments or to cloud public discourse with trivialities, but I'll ignore those issues for now.)
2. We're not entitled to out a person just for taking anti-gay positions on issues like same sex marriage, adoption, or the right to serve in the military. To do so would be a form of blackmail. Some activists argue that anyone who advocates anti-gay policies thereby becomes fair game for outing. That standard is too low. Everyone should be allowed to express their opinions on the issues without fear of retaliation. The merits of a policy argument are independent of the sexual orientation of the individual making the case.
3. To merit outing, a politician must explicitly denounce homosexuality as immoral and socially destructive, and campaign on his or her personal moral rectitude, and advocate criminal or civil sanctions against homosexuals. Politicians who campaign on this platform make their sex lives relevant. If a candidate argues that we should vote for him because of his personal rectitude, then we are entitled to demand evidence of said rectitude.
Some people argue that outing is immoral because private sexual behavior is always publicly irrelevant. Santorum's sex would be relevant because it is relevant to his own supporters. By their own lights they ought to want to know. Even Bill Clinton's most aggressive detractors insisted that the actual blow job didn't really matter (it was the lying!). Rick Santorum's supporters couldn't make a similar argument because they are already committed to the premise that the private lives of public officials bear directly on their fitness to lead.
4. Only incontrovertible evidence gathered by legitimate means may be used for outing. It's no more acceptable to spy on people to learn about their sex lives than it is to spy on them for any other reason. Entrapment is still beyond the pale. Finally, it's not okay for activists to publicize information they know to have been gathered in unacceptable ways.
5. Outing is only permissible if the benefits of exposing the hypocrite are likely to outweigh any harms to innocents. For example, if Rick Santorum were consorting with a well-known Washington rent boy or an openly gay private citizen, I'd feel more comfortable publicizing the affair than if he were having a relationship with a closeted private citizen. Likewise, it his outing would be easier to defend if Mrs. Santorum already knew about his behavior. (If her knowledge was established she would be complicit and therefore less of an innocent.)
Criteria 1) and 5) , above are likely to conflict in real life. Moreover, the tradeoffs are very difficult to calculate. This kind of uncertainty is yet another reason to eschew outing in all but the most extreme circumstances.
We can agree that outing is usually wrong without endorsing a categorical prohibition on the tactic. There are some circumstances under which our duty to combat deceit overrides our obligation to respect certain forms of personal privacy.