In other words: Earnest. Sincere. Pompous. Grave. Boring. Complacent. Smug. Self-righteous.
An attitude that grows grim & deadens levity for the sake of values that cannot – and ought not – be questioned, much less put in the context that does not assume them or take them for granted. Seriousness is the first & fatal step towards dogmatism of any type, along with hypocrisy and pretense that’s always found hand in hand with politics or religion — those ideological sinkholes of petty bullshit.
A serious person takes the obvious false step in a comedy or a satire. At best, being serious locks you in as a straight man in the joke and at worst, end up as the punchline of the joke. Being serious is little more than shackling yourself to a position and throwing away the key, robbing yourself all room to maneuver and room for flexibility to adapt to the changing situation.
All seriousness of intent & purpose rest on arbitrary foundations, and is quickly subverted by irony, parody, black humor, or wit. Irreverence leaves room for discussion or interpretation and tolerates varying degrees of conviction — as opposed to “my truth is better than yours” logic.
Bottom line: a life of play, parody, irony and simulation is just as important as a serious one, if not more so.