Indefensible (adjective)

1. Impossible to defend or justify; unjustifiable.
2. Impossible to protect or guard against attack; vulnerable.

Origin:

From in- + defensible.

Examples:

1. The company's actions were deemed indefensible by the court.
2. His behavior was completely indefensible.
3. The country's position on the issue was indefensible.
4. The castle's walls were old and indefensible.
5. His argument was found to be indefensible in court.