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I think it is a matter of privacy what services (that were breached) I used. This site allows me to type in any e-mail I know and to verify whether or not the person did use a special service. It might seem that this information is not too big of a deal, still I'd consider it private. So my suggestion is that the services only sends back a link to the email that shall be checked and provides the results there.
There are many, many reasons why that’s not feasible: https://www.troyhunt.com/the-ethics-of-running-a-data-breach-search-service/
I disagree. Scammers have been able to target special spear phishing attacks on me because they were able to recognizes sites where I have accounts at. Also I am not okay with the fact that everyone with my e-Mail in mind can check out what (breached) companies I do business with. Also: What will you do if pornhub will get exposed? Makes me kinda anxious to know that everyone will be able to see that I use that service (for example).
Last but not least, I live in the EU and I am absolutely certain about the fact that your service violates GDPR. So you might want to reconsider.