Justify, warrant are comparable when meaning to be the thing (as evidence, a circumstance, a situation, or a state of affairs) that constitutes sufficient grounds for doing, saying, using, or believing something.
Justify may be preferred when the stress is on providing grounds that satisfy conscience as well as reason, and usually refers to an action that, unjustified, would be looked upon with disapproval.
Warrant is especially appropriate (see also ASSERT 1 ) when the emphasis is on something that requires an explanation or reason rather than an excuse and suggests support by authority, precedent, experience, or logic.