Understand that there are two aspects to insurance. Liability and Collision. CDW is collision and your credit card should also provide collision. So no need to purchase CDW. Your credit card should cover you for damage you do to the rental.

Probably however far more important is Liability. This could cover damage to another car, another building or another person. your credit card will do nothing here and its doubtful that the car rental agency will sell you anything useful here either.

Most people when renting in the US will be covered by their car insurance for liability. Most states will require that the car company provide a minimal amount of liability coverage. But it may not be very much. So if you cause real damage you may be on the hook. If you had car insurance you would probably have 100K or 250K coverage. But with state minimum coverage you probably only have 15K or so depending on the state.

In Europe however the minimum provided with the rental is much greater. Like a million dollars, so no need to worry there. So you will actually be covered much better in Europe than in the US. If you have a lot of assets that you would not like to lose in a lawsuit should an accident occur then you may want to look for a policy that will provide liability insurance.