For any informed, intelligent person (who I would assume the typical pre-med to be), they would know that doing the D.O. route is not and should not be a back up plan to MD schools. It should be an ALTERNATE route to the same end goal (becoming a physician). The backup plan for gung-ho MD-hopefuls is and always will be applying to a Post-Bacc program or SMP to boost grades. If the problem is one of a low MCAT score, then there are also programs like Kaplan or other courses to help prepare. After taking these courses, and still getting <28 on the MCAT, then their only choices left are D.O. and Caribbean. There is no backup plan here. They weren't good enough to get into MD school, so how can they feel bad about being given the chance to still be a physician? They didn't cut it in the MD world, so what's there to feel bad about? They should be happy that D.O. schools exist so that they can have another chance at becoming a physician. If there were no D.O. schools, or Caribbean schools, there would be a lot less physicians.
If the student's stats are good enough for MD school, and yet they still fail to achieve acceptance, then there are bigger issues at play that they should address. No one is forcing anyone to apply to D.O. school. Anyone, and I mean anyone, with enough time and perseverance can and will get accepted into an MD school IF they want it badly enough. For people like myself, the time and effort needed to achieve such a goal is not worth putting off an acceptance to a D.O. US Medical School. It is not a backup plan for me; rather, it is the only plan because I know my weaknesses and where I can realistically hope for matriculation.