I don't think the issue is attempting a landing on land, but rather that the proposed site for landing (I think they are proposing to use the site originally designed to become 39C before NASA scrapped that location for Apollo Saturn V launches) is so close to other critical infrastructure.
If they landed on some use spot of semi-wilderness like where Russia does landings for the Soyuz spacecraft, the Australian outback, or some other similar sized far from civilization, they wouldn't have any problem with attempting a landing on land. The problem is that the eastern coast of Florida is hardly what I would describe as unpopulated wilderness. The chance of the Falcon 9 landing in Miami or even Disney World is just too great. That is why the pinpoint accuracy is so needed, especially with the suicide burn approach that SpaceX is using for the core recovery.