If you just want to do basic research, then maybe you don't need an MD. PhD programs are just as free and about 4 years shorter. With that being said, there are also many ways that an MD can benefit your research career. Do you want to do clinical research? Research with a biomedical relevance? Research and practice? Research and teach medicine? The list goes on and on. There is no clear cut answer for why you want to do an MD/PhD (although people will try to tell you that there is one). You just have to be able to justify how both degrees are integral parts of what you hope to accomplish professionally. Be confident in your reason for doing it and don't simply try to tell people what they want to hear. Combining clinical training with research training was and is a very innovative way to approach both research and medicine, so don't be afraid to do something innovative with it.
