Actually, I have a good friend who went to Antarctica on such a ship, and the ship stopped, and they were able to disembark and spend some time on the continent. Different cruises have different objectives, and are intended for different levels of adventure. Some are simply sightseeing with elegant accomodations, others are for more adventurous souls.
And I have another friend who went there with a group of teachers and spent several days and nights there. Lived in tents and even swam in the waters.
It's hardly a closely guarded wall of ice. Anyone can go there.
Again, call any travel agent and get some information on these trips yourself, don't just believe what you hear on this site from others who also have never been there.