I think 501c3s should be barred from taking huge donations like that in situations where it's not 100% clear that such a donor couldn't end up personally benefitting from influencing the charity. For example, I stopped giving money to Wikimedia Foundation when Google showed up with their millions. If there is even just a 0.0001% chance that donations from my hard-earned cash will ultimately just end up lining the pockets of billionaires, then I don't want any part of it.
In Germany there is now a party running on a program trying to forbid political parties from taking donations from any individual above €5000 per year, and barring politicians from staying in office longer than two terms of 5 years each. -- This is roughly the standard I expect from any charity that wants to have any shot at getting money from me.
I don't think it's hard at all to imagine scenarios where his other assets could benefit from a player like Signal competing with Facebook, even if Signal is non-profit.
This is similar to how Google Docs competes with Microsoft Office. It hurts Microsoft's cash-generation and thus benefits Google as they compete with Bing.
If Google had been even smarter (or poorer, so as not to be able to afford footing the bill for Google docs entirely on their own), they could have established Google Docs as a 501c3 foundation, benefitting from tax exemptions and donations from individuals and just dominated that foundation through large donations and putting the right people in charge.
This may or may not be an accurate analogy for Acton's true motives with Signal, but I just can't know the truth of it and am therefore not taking that risk with my cash.
In Germany there is now a party running on a program trying to forbid political parties from taking donations from any individual above €5000 per year, and barring politicians from staying in office longer than two terms of 5 years each. -- This is roughly the standard I expect from any charity that wants to have any shot at getting money from me.