You want to use the resources and influence of a large corporation to acheive your organizations goals. They don’t have to be on board with your mission, and it’s arrogant to think so IMO. Why should they let you do it, when they won’t allow it for others? Seems like you feel entitled because you think by default people should support what you’re trying to do.
The flipside of free speech you’re ignoring is that people get to abstain from using their voice in addition to using it.