In case anybody else has no idea what Ashley Madison is: it's an online dating service that seems to be focussed on people who are already in a relationship and cheat on their partners. Or something like that.
I agree that the privacy violation is bad as it is, but I don't see how this is a good example for why it's bad.
I've been doing it for years without problem, it's a lot easier than you'd first think. Markov chain makes the leader of the email address, domain is selected from a random pool.
For things I care about the domains are owned by me, for things I consider spammy I have a round robin of afraid.org aliases which are for all intents and purposes disposable. They are very effective for this sort of thing, but you would be wise to do your research into the history of the domain you're piggybacking to be sure it's not going to disappear.
This trick only works because it's not that popular. If a substantial amount of people started doing it, firms would simply start removing the extra +info that you pad to your address.
This could potentially be solved by using alias emails instead of just adding a tag to your normal e-mail address. I can imagine gmail offering a quick "generate alias" button that creates a EkTG522f3fhgtfh@gmail.com address that instantly forwards to your real address. Obviously you can delete this alias if you find that you are being spammed.
You set up a catch-all on your domain, and just make up whatever@domain.tld whenever you need an address. I have all my domains set up that way. Not even for unique addresses, just for convenience.
"Facebook’s custom audience feature enables you to create an audience using your data such as email addresses and phone numbers. When using Facebook’s custom audience feature, your data is locally hashed on your system before you upload and pass such data to Facebook to be used to create your custom audience (the “Hashed Data”)."
