Yes it is foolish. Just because you may not be going to cancel your cruise does not mean that you will not have delays or that you won't be hurt or get sick on board or on land and require evacuation and medical treatment both of which cost multi thousands of dollars and must be paid before they will even come get you.
God forbid someone should die, you know what it costs to repariate a body? Or is something shoud happen to a family member at home and you have to come back?
Yes get the insurance.