I experienced this with my PhD topic decision. My focus generally is VR/AR and I was considering looking at health care applications or haptic tech. In the end

I experienced this with my PhD topic decision. My focus generally is VR/AR and I was considering looking at health care applications or haptic tech. In the end I decided on haptics because it seemed more interesting however I have often thought my research could have had more impact had I chosen healthcare. Since starting, my haptic research has subsequently opened up doors into possible health applications and research anyway. This was effectively a middle ground because my research is what I want to do but I can still contribute to something that feels objectively more important. So based on this, my suggestion would be to do what you want, and see if you can find applications in things you think should be worked on.