Comment by Nasrudith

The simplest way to put I can think of is a silly set of two hypotheticals.

Imagine mer-people or aliens existed and started armed raiding marine shipping. That would be would be a hostile act of war. Declaring war on the mer-people would be a shame but justifiable in self-defense.

Imagine instead they were decrypting communications and using it to decipher and view our content. The other would basically be acceptable as part of a first contact protocol and exploration as it involves trying to figure out the basics of communication protocols of an 'alien' species. Declaring war on them in response would be a vastly disproportionate act of aggression for violating laws that they had no way of knowing they were subject to and literally could not possibly know.