The Catholic Church works very hard to supress gay marriage everywhere in the world, and has done a lot more harm to our society than Prop 8 ever would have. The Catholic Church is supported by tithes from their members, which are generally required.
By this same logic, should they not be arguing for the firing of every Catholic employee, who ostensibly spend 10% of their income received from the company to the same end?
So, a Catholic who actively tithes, should not be allowed to be CEO of Mozilla? What about a Lutheran that actively tithes? Both of these organizations work directly to prevent gay marriage, and that money goes to amplifying that cause.
The ELCA doesn't actively attempt to prevent gay marriage. They permit ordination of gays an lesbians, the NALC (a group that split from the ELCA specifically over this issue) and the LCMS (which split earlier) don't.
What I'm saying is that not all Lutheran denominations work directly to prevent gay marriage.
I would make the argument that contributing the Catholic church is far worse for homosexuals, children, women, and the planet than Prop 8 ever could be. But then again, that's why I don't go around making check lists of appropriate contributions for everyone in my company around me...