Some politicians are crooks. They should be voted out, investigated, prosecuted and publicly scorned.

"Everyone cheats" is something cheaters say to (a) feel better about themselves and (b) try to get other people to ignore their cheating when they get caught. Don't believe their lies. Most people don't cheat.

In studies of cooperative behavior, most people choose to cooperate, and the key predictor of whether someone will cooperate is whether they believe other people will choose to cooperate. Cynicism is permission to defect.

Defectors must be punished.