A "prison fantasy" is attractive from the perspective of one who as freedom of choice to "call the scene off". It's kind of like "rape fantasy". Even in a safe, sane, consensual SM play scene, these fantasies can be quite powerful, and are nothing like real life.
In the real world, where you cannot escape, "might makes right", corrections officers are stretched beyond their ability to intervene even if they do catch a prison rape in the act, may not be able to intervene for their own safety, the reality is much more stark and barbaric.
Some of the nicest, hottest guys I met while bringing a rehabilitative outreach into a prison were in for violent or murderous crimes.
Even dressed in my loose fitting long sleeved and baggy clothes, I felt like I was being eyed by hungry animals when I was passing through the lock up area.
Rape Fantasy scenes can also be particularly difficult to stage so that the fantasy "rapist" does not inadvertently become charged with sexual battery or rape. A signed consent agreement witnessed by a notary, sealed in a tamper-evident envelope within a tamper-evident mailing envelope, mailed in advance to an address and left "unopened" until the scene happens and ends (without incident), followed with a signed release witnessed and signed in the presence of a notary are perhaps about the only precautions that a "rape fantasy" top can take to prevent unwanted legal consequences. And even then, no guarantees.
Remember, you cannot contract to do something illegal. And, in the course of a scene, if the "victim" wants to take back their right to say "No", then "No" still means "No".
Too much risk for me. I wouldn't engage in anything like this. Besides, violent sexual activity is not my bag.