It is very easy to do something negative to try and show how intelligent we are.
In an interview between Simon Sinek and Adam Grant they talk about how there can be a tendency to be negative about other people's work to promote one's own intelligence:
When I mentor doctoral students the only thing they can ever do when they read a paper is tear it apart. And I'm thinking, ok ... some of the smartest people in the world in this field wrote this paper. It got through the standards of our top journal, and you a second year student think it's garbage. What's going on here? I think we have a culture where you learn that you signal your intelligence by tearing other people's work apart. And I think it often takes much greater intelligence to build an idea than it does to destroy it.
I think the quote above could be extended to "it often takes much greater effort to build something up than it does to destroy it". A classic example is building - it can take months to build a building and only moments to knock it down.
Early in my career I would be very critical when reviewing other peoples code - not of them directly, but of the code they produced. It wasn't me consciously trying to show my intelligence but looking back in hindsight there may have been an element of that - a need to justify my role. At the time the motivation was to ensure the code was as good as possible but I guess it could have been seen in another way.
We see this to an extent in the media, certainly the British tabloid press. It is much easier for them to be negative and critical of celebrities to sell their papers than to be positive and build them up.
It is also said that "sarcasm is the lowest form of wit". It can be very easy to make fun of someone in the form of sarcasm. It is much more difficult to say positive things about someone - it takes an effort to step outside some social norms. We can feel uncomfortable telling someone how great they are directly to them.
For me one of the turning points was coaching my son's football team. I coached them from the age of 7 to the age of 12. My aim was to always look for the positive in what they did and let them know. It was a conscious decision. If they did something wrong I would always try and put a positive spin on it in some way. I would be looking to encourage rather than discourage. Even now, I find it hard watching youth football coaches who shout at their players, criticizing what they have done even though I am sure the player did their best.
With the negative approach it can focus the attention on the person giving the criticism - they are putting down the other party, making themselves look better. With the positive approach it focuses the attention on the party receiving the feedback.