I never said anything about a specilaty card.... I was talking about a full cavern class from one of the Technical agencies NACD, NSS-CDS, NAUI, IANTD, TDS etc... cavern classes from those agencies tend to be a little more than a platic card.
Regarding the OP, I don't think anyone was referring to technical diving, caves, or penetration diving. What I said was "I believe if two advanced divers want to go into a cavern in-sight of the surface, with proper equipment and exercising good judgement, I don't think they are "tempting fate at all."
Cavern diving is by definition, a form of recreational diving. This means among other things, that divers can obtain recreational-level Specialty Diver certifications in cavern diving from open-water training agencies such as NAUI, PADI, SDI, ACUC and SSI.
Others may argue, Cavern diving is the exploration of permanent, naturally occurring overhead environments while remaining within sight of their
entrances. As you will note, my comment mentioned within sight of the
surface which entails little or no penetration whatsoever. For this type of diving, a "cavern specialty" is not recommended by any diving certification agency of which I'm aware. It's analogous to non-penetration wreck diving.
As an Instructor I promote and have taught a number of specialties (Cavern diving included). If any diver decides to penetrate a wreck, cavern, pipeline, anything, further training is required. I do not however take a "you're gonna die" attitude if someone pokes his head into a cavern or a wreck. It's all about diving within your capabilities and exercising good common sense.