It’s perfect topic for a flame war. But imho blocking airports ends up in more traffic overall because planes must be re-routed. Is this not opposing original goal?.. or the goal is not saving climate at all?..
The main discussion is whether this kind of action will create the intended result.
Even dumber is annoying and inconveniencing random bystanders that have literally no way to influence the problem, like these protesters are doing to the travelers here. Nonetheless, there is no way to avert the coming climate catastrophy without forcing almost everyone to change their behavior.
Wherever that has any chance of happening is a different story altogether.
And you're mistaken wrt what I labeled dumb: I specifically phrased it in the context of actions, not people.