Manny, it may also be illegal to release him. Not sure what fines etc. if you were caught, but the fear of ending up with "Bubba" as your cellmate, who has eye's on you, would be enough for me not to do it. 8O
You also probably have non native animals in your tank. The crab could carry something non native into the ocean such as larvae,polyp or something in its stomach. Its a bad idea for so many reasons that we can only begin to understand. WHy take the chance. Make him into fish food or deep fry it for a snack.
C'mon guys, this shouldn't even be a discussion. The act of releasing an aquarium animal into the wild is just plain irresponsible. Unless of course you're a collector in Fiji and get all of your livestock and rock from snorkeling and diving.