You have to love this sentence "We want Prime to be such a good value, you’d be irresponsible not to be a member."
I like being that irresponsible one. Though it is impressive that Amazon has turned a delivery fee - that most people don't like paying - into an exclusive subscription service. A service that customers fall over themselves to sign up for when it's offered at a discount.
However, by purchasing 'shipping insurance' one can normalize the cost of shipping similar to the way one normalizes the cost of car accidents through car insurance.
There is a virtuous circle too that is the opposite of moral hazard typically incurred by insurance companies as having certainty of cost makes risk taking less costly. Similarly, if shipping is free, then people order more things, creating economies of scale that reduce shipping costs, enabling amazon to make more profit, or price prime cheaper.