>they are charging their customers after their customers have deactivated a service (destroyed a VM)
They are charging their customers for the number of minutes it takes to safely destroy the VM. This is not a charge for something coming 'after'. It's fundamentally a charge for their actual server use, not a bonus fee.
>What sort of mental gymnastics are required to make that a reasonable choice?
They aren't charging for security, they are giving you the option to buy less server time if you don't need security, or handle it yourself by wiping only the sensitive files. There are no mental gymnastics here.