It is not true that you should always take Medicare Part B. It is probably true that most people should take it but the Medicare beneficiary demographics are starting to change radically because of the continuing increase in the Social Security full retirement age so all the old rules are also changing. There is a lot of just plain bad information on the Interent in general and particularly about Part B (and I’m leaving out my standard criticism of the typical nonsense that Part A doesn’t cost you anything).
In fact there is no requirement that you enroll in Medicare ever… age 65 or otherwise. I think you would be crazy not to given that you paid for it for 50 years but there is no requirement that you do it. (But you will be signed up for Medicare automatically if you start collecting Social Security. But presumably if you are against signing up for Medicare, you are against signing up for Social Security.)
And Medicare does not pay the costs for true catastrophic illnesses or for any custodial nursing care – prolonged or otherwise