I wish you would give Brendan the chance to repent.
First of all, and most importantly, it's unlikely they are going to shitcan him as CEO.
Second, he has not spoken about his motivations for donating to Prop 8. If he was doing so in pursuit of abolishing the marriage institution altogether, I consider that very different than doing it because he only wants straight people to marry. (Since this is a politically charged issue, I will say that while I am personally in favor of abolishing marriage altogether, I think actively working to deny gays the right to marry in the interim is an exceptionally absurd idea.)
Third, his views may have changed over the years.
If he came out saying he was wrong and donated 10x the amount he donated to Prop 8 to a LGBT charity, I would consider that a win. There are ways to make this right without shitcanning him.