Everything Old Is New Again: Targeting Pro-Revolutionary Advocacy in 1952, Opposition to Gay Marriage in 2019
Beto O'Rourke channels the past.
In 1952, voters amended the California Constitution to deny tax exemptions to people who "advocate[] the overthrow of the Government of the United States or the State by force or violence or other unlawful means or who advocates the support of a foreign government against the United States in the event of hostilities."
But, said the Supreme Court, in an opinion (Speiser v. Randall) by Justice Brennan:
[A] discriminatory denial of a tax exemption for engaging in speech is a limitation on free speech…. To deny an exemption to claimants who engage in certain forms of speech is in effect to penalize them for such speech. Its deterrent effect is the same as if the State were to fine them for this speech.
The [government is] plainly mistaken in [its] argument that, because a tax exemption is a "privilege" or "bounty," its denial may not infringe speech…. [T]he denial of a tax exemption for engaging in certain speech necessarily will have the effect of coercing the claimants to refrain from the proscribed speech. The denial is "frankly aimed at the suppression of dangerous ideas."
The Court ultimately concluded that, even if tax exemptions were denied only for speech that already falls within a First Amendment exception and could thus be criminally punished (as, for instance, intentional incitement to imminent and likely violence would be unprotected today), the government had to bear the burden of proving that the speech is indeed constitutionally unprotected. But the Court made clear that viewpoint-based tax exemptions for constitutionally protected speech are unconstitutional.
Now, in 2019, Beto O'Rourke has publicly endorsed the view that "religious institutions, like colleges, churches, charities, should lose their tax-exempt status if they oppose same-sex marriage."
I should note that it would probably be constitutional to deny organizations tax-exempt status if they discriminate in tangible benefits—such as university admissions or access to services—against gays or lesbians, see Christian Legal Society v. Martinez and Bob Jones Univ. v. United States, or against people in same-sex marriages. (Whether that is a good idea, and how people who belong to traditionalist religious groups should view O'Rourke based on this, is a separate matter.)
But the question to which O'Rourke answered "yes" was specifically about groups, including churches, opposing same-sex marriage, and not just discriminating in hiring, admission, or charitable services against gays and lesbians. (Press coverage reflects that, see, e.g., "O'Rourke: Religious institutions should lose tax-exempt status if they oppose same-sex marriage," The Hill [Julia Manchester].)