The antonyms for the word "un-justified" include "justified," "valid," "reasonable," "logical," "reasonable," and "defensible." If an action or a decision is justified, it means it is well-founded, well-reasoned, and backed up by sound evidence or argument. The opposite of unjustified is not only valid, but it is also supported by facts, logic, and similar forms of evidence. When an action is reasonable, it means it is sensible, rational, and justified. In essence, any antonym for the word "un-justified" must denote an action or a decision that is morally, ethically, or logistically justifiable.