So, you're saying then, that they should go through the donations of every employee, ever, and fire anyone who donated to a cause that a sub-group of employees disagrees with?
With this line drawn, it's not about going through and ratting out people who donate to stuff you don't like, and it's not about limit free speech. This is about supporting human rights, and more specifically to the private company, maintaining a workplace that is inclusive to everyone, and a vision for the company that everyone can get behind.
Yes, everyone has free speech and should be able to support whatever they want, but when you support oppression, I think it's completely fair that there is backlash and questioning of whether you should be part of, and benefitting from, a inclusive group. The employees have every right (freedom of speech, remember?) to voice opposition to you in your role, because it really does affect everyone in the company.