I am sorry, I do not have good news. Apparently watching or reading incest porn is not against any laws - state or federal - providing there is no child porn involved. If any of the porn is involving or exploiting a minor child.
If your husband is watching incest videos that include minor children I would strongly advise you to go to your local police and report this. Not only is it against the law but it is a known fact that people that watch child porn are much more likely to offend a child.
If this is not a child porn issue, then by law there is nothing you can do to stop it. You have the right to file for divorce if this is a major issue in your marriage, with his actions most Judges would feel you have a justifiable issue for leaving. If you have young children in the home, you may want to consider their safety in the home as well.
I wish you the best
DISCLAIMER: Answers from Experts on JustAnswer are not substitutes for the advice of an attorney. JustAnswer is a public forum and questions and responses are not private or confidential or protected by the attorney-client privilege. The Expert above is not your attorney, and the response above is not legal advice. You should not read this response to propose specific action or address specific circumstances, but only to give you a sense of general principles of law that might affect the situation you describe. Application of these general principles to particular circumstances must be done by a lawyer who has spoken with you in confidence, learned all relevant information, and explored various options. Before acting on these general principles, you should hire a lawyer licensed to practice law in the jurisdiction to which your question pertains.
The responses above are from individual Experts, not JustAnswer. The site and services are provided “as is”. To view the verified credential of an Expert, click on the “Verified” symbol in the Expert’s profile. This site is not for emergency questions which should be directed immediately by telephone or in-person to qualified professionals. Please carefully read the Terms of Service (last updated February 8, 2012).