I think you hit the nail on the head here: offering the option to buy less server time if you don't need to wipe data is probably reasonable.

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.