The concern was that performing a slingshot around Earth with a RTG-equiped probe has risks. If early in the mission the probe loses the ability to guide itself, then the probe may be off course enough to hit Earth.<p>The Cassini mission to Saturn did this with an RTG, and there was a significant outcry about the plan.[1]<p>[1] <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Cassini–Huygens#Plutonium_power_source" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Cassini–Huygens#Plutonium_powe...</a>