I'm pretty sure if technology could exist that would be able to destroy our galaxy...some other aliens would've done it already.

Not necessarily. Someone having the technology to be able to do destroy a galaxy, doesn't preclude they have it to use it that way. I would think it just as likely their intelligence, which allowed them that level of advancement, would also allow them to know life in our galaxy has as much value as life in any other galaxy, including theirs.