There is of course always the possibility that intelligent life has already found us, took a peek, watched us for a few years, and then used their advanced technology to Trump Wall our section of the galaxy off from the rest of the universe
.
"What are they like, Zarglarb?"
"Oh they're terrible. Just terrible. Most of them mean well but what a ****ing mess..."
"Are they dangerous?"
"To us? Not really, no."
"Do we want them to join the intergalactic community?"
"Oh HELL no. No, no. Just... no."
"OK... give them a couple of dozen solar systems to explore and leave them alone I guess."
Then they set up some sort of massive energy bubble around us that filters out all signs of life from outside, and we can never pass.
