Humans are certainly not too stupid. Alien life is definitely extremely rare. And when something is rare, nothing will be considered too stupid. The analogy of a child randomly calling other houses doesn't apply, because children on this planet are not rare, they are common.
Space travel is pure luxury. You will only travel to other star systems if you don't have any other problems left. It will never be used to mine resources because it costs more than it gains, it will also never be used to relocate the planet's population in case the planet's fucked up because other suitable planets are way too far away. It's highly likely that space travel will be so costly and time consuming that anything other than exploration is out of the question.
Whoever visits our planet is going to be an explorer. And whoever visits our planet is going to be an enlightened mind who will not just start a war or dissect people. They will also not evangelize other cultures, because the situation is not comparable to the colonization and sea faring in the 14th to 18th century. You have to keep in mind that we already know that it was wrong, and we wouldn't do it again, and it's already certain that a highly developed space faring race will be far beyond fundamentalist religion, because - as we already can see - scienctific exploration changes fundamentalist religion to something a lot
I don't think NASA astronauts would go around invading other planets, and so I don't think any alien astronaut would do it.