It's easier to criticize, both cognitively and socially.

We see flaws and downside more readily, because we're naturally risk averse and because there are more ways for things to go wrong than right. Having a point to make makes people feel good and smart, but most of the points we think of will be critical.

When we affirm something, we attach more of our identity to it than when we criticize. Then, when someone else is critical of that thing it feels like an attack on us. Cynicism is safe.