In spite of the fact that the RTG heat modules containing the Plutonium can survive reentry, critics argue that many deaths would result. The Plutonium in the RTGs would have to be miraculously ground into dust of exactly the right size to be inhaled into lungs and somehow delivered to the world population. Even in this improbable case, a few pounds of Plutonium is small compared to the several thousand pounds that were vaporized into the atmosphere during the decades of atmospheric nuclear weapons tests around the world. If there are a few thousand cancers from this cold war source, they are hidden in the millions of cancers people get from other causes. Critics point to the Russian disasters, but they have been putting nuclear reactors in orbit, not the benign heaters that generate electricity as have been successfully used in more than 20 NASA missions.
Nuclear reactors do have deadly products that can contaminate areas they fall onto.
The fuel capsules of the RTGs however, emit only alpha particles which are easily stopped by shielding. You could hold them in a gloved hand with little harm. An RTG is presently the only known practical way to reliably generate the 800 watts of power needed for this mission over its 10 year lifetime. NASA is wary of any military activity in space, such as the recently proposed Star Wars tests, since it has so many vulnerable spacecraft in orbit that could suffer from military actions. The Cassini project is a good one that is supported by hundreds of students , scientists and engineers in the United States and 16 other countries.