Whenever at least one isotope is radioactive, anything containing that element is radioactive, but with a lower activity, proportional with the natural abundance of the radioactive isotope. Because the isotopic abundance also matters, elements like carbon and potassium have very low activities even if their radioactive isotopes have high activities, because the abundance of their radioactive isotopes is very low.
The majority of the naturally occurring chemical elements, i.e. about three quarters of them, are non-radioactive.
Even if the naturally occurring chemical elements either are non-radioactive or have low radioactivity, otherwise they would have disappeared since the formation of the Solar System, their radioactivity is non-negligible due to the huge number of atoms that exist in every gram of substance.
Inside a human body, during each second, thousands of atoms disintegrate, emitting radiation.
However, almost all damage caused by the natural radiation is repaired, because all living cells have very efficient mechanisms for this. Only at higher doses those are overwhelmed.
I think you the defintion is the opposite, ie that an element is considered radioactive if NO isotopes are stable (ie ALL are radioactive).
https://www.thoughtco.com/list-of-radioactive-elements-60864...
Huh? Care to name 5 non-radioactive elements according to your definition?
Of course, you are correct that the dangers of radioactivity depend on the dose. But your message is diminished by overly emphasizing the radioactivity in carbon and other naturally occurring elements that pose zero health risk and frankly are so very non-radioactive in a relative sense.