there's an option on the donation page where you can opt-in to the ACLU sharing your details with other charitable organizations. (the default is opt-out).

I verified via the wayback machine and the page is the same today as it was when I made my donation. I'm fairly certain I would not have checked that box. I make it a point to read checkboxes very carefully as companies are so prone to anti-patterns to get you to agree to share your info or join mailing lists.

Always possible you donated to another group around the same time...

I also didn't check the checkbox and haven't heard from the other organizations you cite.

Except, you know, they're a bunch of lawyers so any abuse of their own privacy policy is not really going to fly with them, especially from an optics perspective. It's far more likely that you did, in fact, click the checkbox, and just forgot about it than the ACLU deciding to ignore your request and forward your information anyway.

One data point: I have no idea if I checked the box, but I'm a regular subscriber and I've never had solicitation from any of those other companies.

If you check out the donation form, people are opted-out of that by default now. (Not sure how it was previously.)

I don't think you can fault the ACLU? In my experience: I donated a few times in the past and now I am a guardian of liberty (monthly donation) and I've never gotten any solicitations from any other charity/organization. However in college I never donated to any charity (wasn't stingy, just prioritizing being able to eat and pay rent at that time...) And I got piles and piles and piles of solicitations for those organizations you've mentioned. I don't know where the "leak" came from.

Yes, I experienced this as well, though it was about 8 years ago. I was really disappointed in the ACLU, I would have thought of all people they would be the last ones to sell off private information. It bothers me that all these groups have spent more money on sending me mail in the ensuing years than the original donation amount to the ACLU.

At least now it seems like they let you opt out.

This is a problem in the non-profit industry that should get addressed, especially given younger generations are less likely to respond to mailers anyways.

As an employee of an old world charity trying desperately to connect with younger generations, I completely agree with you.

Our organization struggles to unsubscribe people from mailing lists. It's kind of ridiculous.