Shadyness is relative. I felt quite ashamed of having an account on some of those sites that HIBP considers "non-shady".

If someone has your email address, it's often not very hard for them to determine whether or not you have an account on a particular site. (Try to register with that email, and if the sign-up form complains, then you probably do have an account there.)

That said, if you're still concerned there's always https://haveibeenpwned.com/OptOut

Would be neat if one can opt-out a domain. I.e. I have a domain that's essentially a catch-all for signing up with per-site unique emails.

Can't hurt to send Troy an email. Probably would be a useful feature for companies, too. Could be achieved relatively easily w/ DNS validation.

There is a big difference between checking every service one by one and scanning them all at once.

OptOut is indeed what I needed, thank you for the idea.