Being charged with a crime and being found not guilty can still bankrupt you and consume years of your life. You can't be charged with a crime that isn't on the books.
> You also can't stop criminals with a crime that isn't on the books.
If you make this sentence mean anything at all, which requires redefining "criminals" as something like "moral wrongdoers, independent of whether their wrongdoing is actually a crime", then it still isn't true, as the existence of a law prohibiting an act is neither necessary nor sufficient to create disincentives to committing the act.
Defining "criminal" to mean wrongful rather than illegal doesn't actually help you. Aaron Swartz or graduate students publishing crypto code would not be doing anything wrongful either. And no one is suggesting that we remove the laws against unarguably wrongful things like fraud or homicide, none of which could plausibly be used to charge any of those people.
What dictionary does your definition come from? According to multiple sources[0], the closest match to your definition (American Heritage's "Shameful; disgraceful: a criminal waste of talent.") is typically used in a figurative sense ("that spinach dip is criminally awful").
