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why in the world scientists are wasting time and effort making things like that when they can be doing things like finding cures for as-yet uncurable diseases is beyond me.
If it weren't for some failed unrelated experiments, we wouldn't have antibiotics to begin with (at least at the time when we figured it out).
Every science is of relatively equal importance. Focusing on one field alone will blind us to many other things, and in many ways they are inter-related. Also, not all scientists can work on the same fields, since they specialize in different areas. I wouldn't want an astrophysicist working on cures for diseases (for example), because it would probably involve fire and projectiles.
When it comes to nano-robotics and this sort of thing with engineering molecules, the first thing that comes to my mind is medicine actually, because many predict that they will be used in the future to keep people healthy in many ways. Going through the blood stream, taking care of clots, and other stuff along those lines. In the process of developing this technology there are many steps, and these seemingly random creations are actually experiments to see what is possible with our current understanding and where this technology can go.