The silliness of sin comes not in the consequences that our sin deserves, but in the lack of thought or carelessness with which we regard those consequences.
If someone decides to do something dangerous, but they’ve weighed out the risks and consequences and then gone forward, that’s one thing. It may be a good or bad decision, but at least it was thought out. The consequences weren’t ignored, but instead deemed worthy of the risk/reward for the decision.
In sin, however, we decide to do what is dangerous and ignore the consequences and cost. In truth, if we thought about or took seriously the consequences of sin that are promised to come, we’d never make the decision to go forward with them. Scripture says this is foolishness.
This is the silliness of sin.