You point is true for all organisations that cover many issues, and do not concentrate on one single small issue. You end up not donating to anything, even if your donation would have a large net positive.

Tagging money for specific issues is problematic because the organisation doesn’t change its budget percentages for small donations (money is fungible), and organisations find tagging difficult to manage [TODO insert article link here].

Organizations that say that they let you donate to fund specific issues are fooling you, unless the amount you plan to donate is huge. The reason is that money is fungible. Let's say I need $200k to fund issue A, and $200k to fund issue B. You say that you want to support only issue B. Fine, I just put your money in the issue B bucket and move a corresponding amount of unrestricted funds into the issue A bucket. Unless almost everyone restricts their donations they can always do that. They can backfill any unrestricted money to fund any of their priorities that are, for some reason, less popular with donors.

Call them and ask. There is usually a fund manager who can direct the money into different causes at the benefactors wishes. Now, if you only donate a minimal amount that will go in to the general fund. They wouldn't expend the same energy for a $35 donation that they would for a $3500 donation.