The danger depends somewhat on the type of radioactive material used and how much of its radiation is alpha, beta or gamma, it's toxicity (independent of its ra

The danger depends somewhat on the type of radioactive material used and how much of its radiation is alpha, beta or gamma, it's toxicity (independent of its radioactivity, plutonium is one of the most toxic substances in existence), half-life etc. But really, the main problem with proliferation of RTGs is dirty bombs. If you used them in cars or homes you can imagine the kinds of issues you might have with a serious collision or wildfires. In any case, people actually once proposed cars like that! https://en.wikipedia.org/wiki/Ford_Nucleon https://en.wikipedia.org/wiki/Ford_Nucleon