What sort of mental gymnastics are required to make that a reasonable choice?
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.
Now, the problem here is that DO turned that choice around, and are therefore not providing security by default, but offering you the option to pay more to get it.
Additionally, this is poorly advertised (the API docs do not clearly state "Your data may be accessible by other users!"), and that explains why many customers are (reasonably) a bit pissed at DO.
Besides we are not talking about a high margin business here. $5 vms when most providers are charging 4x times that. Its not unreasonable to expect that your going to have to pay for extras. Similar to a budget airline, you get what you pay for. You want a service that includes that cost in your other fees... then use AWS, rackspace or one of the 1000s of others.
Seriously, there should not be an option "Shall we pass your latent information onto the next user?" left active by default. If people want to save that trivial amount of money, then let them turn off safety themselves.