Prison is also a deterrent for future offenders, if everyone is knows/feels all they will loose is their license to practice finance then you will have lot more financial crime than there is.
You cannot stop murder, rapes, petty theft etc with punishments you can deter white-collar crimes which are executed with a lot of forethought as this is a critical decision making factor.
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To be clear I meant loosing financial license is not same as loosing medical or legal license, no one is spending 10 years of education and hundreds of thousands of to get one, so it is not much of deterrent to threaten loosing it.