If you say that a statement, action, or idea is indefensible, you mean that it cannot be justified or supported because it is completely wrong or unacceptable. She described the new policy as `morally indefensible'. defensible
incapable of being justified or explained (of theories etc) incapable of being defended or justified
{s} inexcusable, unjustifiable; impossible to defend, cannot be protected by military means
Not defensible; not capable of being defended, maintained, vindicated, or justified; unjustifiable; untenable; as, an indefensible fortress, position, cause, etc