Medical insurance with guaranteed policy wording: the only suitable option?

Certainty that existing benefits will be there when needed (contractual rights) is vitally important for all types of life and health insurance.  It’s integral to the promise of guaranteed renewability inherent in life and health insurance. 

Without the guarantee of life and health insurance entitlements, how can there be any confidence in life and health insurance as a long-term concept? 

Imagine if life insurers could simply impose (on existing policyholders) new exclusions on life cover for death by certain illness or death by motor vehicle accident, for example.

Life and health insurance is not like fire and general insurance, where policyholders can relatively easily switch to another insurer to maintain or improve benefits.  Poor health will very likely not permit a switch.