The co-founder publicly stated he made the donation on social media. What made him obliged to disclose this? He seems rather proud of it, in fact.

As a result, people feel they may have a moral obligation to not funnel money to him. Your stance also doesn;t really line up with your examples like

Or say your customer base for any reason is in large part Vegan, should you tell your employee’s to stop buying meat? Should they stop taking money from the non-vegan customers? How is anyone going to navigate this?

You don’t mention the specific problem you have with this, which would be mandated disclosure. By your own words, this is perfectly fine since people can chose the reasons “Anything, including having no reason at all, obviously.” to not do business with someone so I’m not sure why it’s a slippery slope to you.