  We revisit here a previous argument due to Wald showing the impossibility of
turning an extremal Kerr-Newman black hole into a naked singularity by plunging
test particles across the black hole event horizon. We extend Wald's analysis
to the case of near-extremal black holes and show that it is indeed possible to
destroy their event horizon, giving rise to naked singularities, by pushing
test particles towards the black hole as, in fact, it has been demonstrated
explicitly by several recent works. Our analysis allows us to go a step further
and to determine the optimal values, in the sense of keeping to a minimum the
backreaction effects, of the test particle electrical charge and angular
momentum necessary to destroy a given near-extremal Kerr-Newman black hole. We
describe briefly a possible realistic scenario for the creation of a Kerr naked
singularity from some recently discovered candidates to be rapidly rotating
black holes in radio galaxies.
