What you are saying is exactly what I'm saying. There is no disadvantage for just doing a pure MD. As long as you fulfill your training as a scientist at some point. And by the same token, I don't see the advantage of doing a PhD in substance, because a post-doc basically the same thing as a PhD, except with more focus and a higher paycheck.
I have heard that people who only has an MD can get turned down more easily when they apply for a grant, etc. There may be a small point for getting a PhD if one wants to focus on pure basic science. But all in all, I think in academia the name of the institution carries more weight than your degree. For instance, I would speculate an MD researcher from UCSF would have a more favorable impression than an MD/PhD from Michigan State. This is simply because most of the people on NIH's grant review committee are from big name institutes (same for editors of big journals etc.)
To make this discussion more productive, I think i've made some arguments suggesting that someone who gets into an MD program with a really strong research program in a particular area and a very high institutional reputation should probably forego an MD/PhD program at a less reputable institution. Keep in mind I'm talking strictly about the reputation of a particular field.
secondly, I think those who are interested in research but can't make up their minds shouldn't be rushed into MD/PhD or PhD programs. First of all, I don't think there is a disadvantage if you go for the "late-boomer" route. Secondly, rushing into a PhD program may be a really bad idea, especially for young people who constantly change their minds. If you have an MD and decided research's not for you, worse comes to worst, you drop out and become a highly paid, well off admired physician. If you have only a PhD, you either get a job in the industry or get a teaching job in a college, jobs that are much less well compensated and socially valued. (Obviously I think social values have their intrinsic and fallacious bias, but that's besides the point.) Instead, be happy that you got into a med school! You can always do research once you become a doctor.
Originally posted by cmz
For the MD-only HHMI investigators... all I have to say is that MOST of them did a residency + fellowship and a ****-load of post-docs to get where they are. They might as well have done a PhD.