To begin, I'm not arguing nor have I come to any conclusion related to whether a fine or prison time is appropriate, however a fine/financial cost is very relative to a person's financial situation, and it is also more subtle, and perhaps also in some areas someone could simply declare bankruptcy or a fine will have no impact if their life is already "in the shitter." Prison on the other hand is a concrete/tangible separation from a person's regular life/routine, and so it's guaranteed to not be subtle - however as I replied elsewhere in this thread -
https://news.ycombinator.com/item?id=18150041 - how prison affects someone can vary greatly and be much more detrimental than what a financial cost could potentially have, and I think it would be immoral to not properly account for this - if prison time is going to be allocated; another variable to account for is around the world "prison time" has great variability as to the conditions someone is put into, likewise with the social/safety constructs of taking care of people, or not.