The Ghost Rays are very interesting and eerie enemies, but they seem like a missed opportunity as passive creatures - and passive creatures that don't even attempt to retaliate or escape from danger in any way.

While there are many mods that allow you to make neutral monsters hostile (let alone using a different mod to just spawn them as their aggressive version with NBT), there are no mods that are able to make passive creatures neutral or hostile.

Having them be neutral by default, or have this be an option that could be enabled, allows players and pack makers to potentially make these creatures neutral with dangerous effects, or even hostile monsters, without too much effort on your part, and without removing your ideal vision of the ghost rays as eerie but peaceful creatures.