Nanotechnology has a lot of potential for good in this world, even when it comes to having it inside of your body. Unless you have a serious religious issue with having robots working to repair the problems you might have inside, there should really be no issue at all, so long as the robots remain under the watchful eye (and careful hand) of the people who are trained to keep you safe. But of course, it will require you to do something which may be a little frightening — having microscopic robots injected into your system where they may remain for a long time. However, the potential for good far outweighs the potential problems.
Just imagine what would happen if you could have an artificial “boost” to your immune system. Imagine the potential when it comes to unclogging your arteries. Nanobots could be sent in and could essentially act like a miniscule construction and demolition crew. As they clear out your arteries (by breaking up the plaque into tiny enough particles that it can be flushed out), they may extend your life span by decades. Imagine being able to head off a heart attack when you are only in your 20s and are not suffering any kinds of symptoms. The potential for preventative medicine using these tiny wonders is potentially unbelievable.
Now imagine that the nanobots were going to be sent in, not to break up something but to actually repair it. While the platelets in your blood are intended to fix the tiny tears which will inevitably develop sometimes, they do have their limits. Nanobots, however, may be able to function a hundred times faster and repair levels of damage that would stress your platelets far beyond their limits. Imagine having a terrible hemorrhage and having nanobots sent in to essentially rebuild the structures of the blood vessels inside your brain. No surgeon could work on such a tiny level as they can.