All that glitters is not gold.
This fits relatively well, "Barack Obama says nuclear energy may very well be able to facilitate immortality, but, unfortunately, all that glitters is not gold:
Ironically the very same (experimental) treatment is known to cause an ailment, for which the only cure is death, in any untreated individual who comes within 500 feet of a patient on the regimen."
Also, as a matter of personal principle i feel obligated to point out that the science suggests that of all energy sources, Nuclear seems to have the best ratio of energy output to safety (and practicality in terms of there being no shortage of nuclear fuel).
Less appropriate good bad idioms:
The road to hell is paved with good intentions.
What goes up must come down.