Of course you're dead set against any other kind of intelligences contacting us, even if you woke up one morning with a "message" written on your forehead.......
Remember, WE sent out images and mathematics into space as a central point for contact.
WE did.
Therefore we think it's possible.
What do you think?
They'll send us a letter or ring us up on the telly?

Try thinking if you were another form of intelligence, and you wanted to contact us humans.
How would you do it?
(My question would be.....WHY??) LOL

>". If they really wanted to impress us, let's see them carve a pattern on the face of El Capitan, or something equally tricky."

Yeah, I agree. A friend of mine once told me ten years ago, that people won't sit up and notice "crop" circles until they start etching them onto our highways and the sides of buildings.
But you see, that would be too aggressive.....AND threatening.

There still is SOME mystery as to who we are and why we're here and what our Universe is about.
You have to accept the fact that YOU don't know EVERYTHING, that you just have an opinion about it.