I am pretty sure that Fabricate Hook only creates a hook, but no actual secret UNLESS there already exists a secret, in which case you may learn it and get the hook from that real secret. But if you're trying to Fabricate on a goody-goody with no secrets you don't get some fake secret you can then choose to either expose or blackmail with.
Example: I tried to Fabricate a Hook on my cousin. I succeeded and the game told me "hey, turns out she's a Deviant, just tell her you know" and awarded me a hook. In the Hooks & Secrets screen I could see that I had a strong hook on her and the reason was listed as her Deviant secret. But at no point was I allowed to expose that secret, because the fabrication process was equivalent to me having blackmailed her over it, and you can't expose a secret you've used for blackmail.
When I've succeeded at Fabricating on a person with no secrets, I've always gotten some vague hook description like "threatened," with no actual secret attached to it.
So if you just want to force someone into accepting arrrest, Fabricate will get you a hook to do that, but if you want to EXPOSE them as a criminal to avoid tyranny from punishing an upright citizen, Fabricate will NOT do that for you. You have to find some real dirt on them. At least, that's my experience.