Blackmail is defined as:
The action, treated as a criminal offense, of demanding money from a person in return for not revealing compromising or injurious information about that person.
A crime – a felony under certain conditions – blackmail is coercion involving threats of physical harm, threat of criminal prosecution, or threats for the purposes of taking the person’s money or property.
Examples include threatening to expose injurious information, usually obtained by subversive methods, about someone unless they pay you money.
If, for example, you’re a blogger that has posted an enlightening post and the person it’s about comes to you, BEGGING you to make some deal, any deal, to get you to take it down, THIS IS NOT BLACKMAIL.
If they wheel and deal, BEGGING YOU to make a deal to remove information which has already been made public knowledge, information which was public information to begin with, THIS IS NOT BLACKMAIL.
If what they agree to pay you is money they owed you in the first place THIS IS NOT BLACKMAIL. It’s justice.
If you hold up your end of the deal and remove the information you posted, asking only that the scurrilous activities that it reveals not be continued or repeated, You’re in the clear. You’ve held up your end of the bargain.
If the other person reneges on that agreement and continues whatever activity was described in that original post, THEY have broken the deal. You are no longer bound by it. So if you restore that post, and create subsequent posts about the same illegal activities being perpetrated by the same person in order to warn potential victims, you are not guilty of any crime. You are committing a public service intended to assist the public in general.
And if the person that broke the deal is the type that likes to bilk victims out of hundreds of dollars by accusing them of breaching a contract that wasn’t legal in the first place, it’s not only a public service, it’s poetic justice.
So if you see somebody screaming “BLACKMAIL!!” about a deal they broke themselves, take a good hard look at what they’re trying to cover up. You can bet your bottom dollar (if they haven’t stolen it yet) that the louder they scream, the more they have to hide.