I fail to see how this is good? These batteries are being sent into space to explore our solar system. Without them powering some of these spacecraft becomes extremely difficult or impossible.
I don't think that fear is in the end warranted, but as fears of such things go, it is more justified than many.
from Wikipedia: To minimize the risk of the radioactive material being released, the fuel is stored in individual modular units with their own heat shielding. They are surrounded by a layer of iridium metal and encased in high-strength graphite blocks. These two materials are corrosion- and heat-resistant. Surrounding the graphite blocks is an aeroshell, designed to protect the entire assembly against the heat of reentering the Earth's atmosphere. The plutonium fuel is also stored in a ceramic form that is heat-resistant, minimising the risk of vaporization and aerosolization. The ceramic is also highly insoluble.
it also notes that the LEM on Apollo 13 carried a RTG, and there was no sign of contamination after it re-entered and landed in the Tonga Trench. And that was a extreme outlier due to the high velocity it re-entered at being it was following a trans lunar trajectory.
The people who protest these things expose themselves to orders of magnitude greater risk on their drive to the protest.