unwarrantable(s = adj.all) indefensible, insupportable, unjustifiable, unwarranted - incapable of being justified or explained;

   Not warrantable; indefensible; not vindicable; not justifiable; illegal; unjust; improper. [1913 Webster]

unwarrantable, adj. indefensible, unjustifiable.

Derivative:
unwarrantableness n. unwarrantably adv.

N  illegality, lawlessness, illicitness, breach of law, violation of law, infraction of the law, disobedience, unconformity, arbitrariness, antinomy, violence, brute force, despotism, outlawry, mob law, lynch law, club law, Lydford law, martial law, drumhead law, coup d'etat, le droit du plus fort, argumentum baculinum, illegality, informality, unlawfulness, illegitimacy, bar sinister, trover and conversion, smuggling, poaching, simony, outlaw, bad man, v, offend against the law, violate the law, infringe the law, break the law, set the law at defiance, ride roughshod over, drive a coach and six through a statute, ignore the law, make the law a dead letter, take the law into one's own hands, smuggle, run, poach, illegal, unlawful, illegitimate, not allowed, prohibited, illicit, contraband, actionable, unwarranted, unwarrantable, unauthorized, informal, unofficial, injudicial, extrajudicial, lawless, arbitrary, despotic, despotical, corrupt, summary, irresponsible, unanswerable, unaccountable, expired, invalid, unchartered, unconstitutional, null and void, a dead letter, lawless, unregulated, illegally, with a high hand, in violation of law.

N  wrong, what ought not to be, what should not be, malum in se, unreasonableness, grievance, shame, injustice, tort, unfairness, iniquity, foul play, partiality, leaning, bias, favor, favoritism, nepotism, party spirit, partisanship, bigotry, undueness, wrongdoing (vice), unlawfulness, robbing Peter to pay Paul, the wolf and the lamb, vice, a custom more honored in the breach than the obser, wrong, wrongful, bad, too bad, unjust, unfair, inequitable, unequitable, unequal, partial, one-sided, injurious, tortious, objectionable, unreasonable, unallowable, unwarrantable, unjustifiable, improper, unfit, unjustified, illegal, iniquitous, immoral, in the wrong, in the wrong box, wrongly, it will not do.