Is Holmes such an imminent danger to society that she needs locked up and cordoned off from our communities?
Secondly, those positions are not mutually exclusive or even intellectually inconsistent. You can think there are too many people in jail general (eg for certain crimes and certain groups in society) and still think that for certain specific cases, jail is appropriate.
Thirdly, as a sibling has pointed out, protection of society is not the only or even the primary reason a jail sentence might be appropriate in a given case. I believe prosecutors believe flight risk is the primary reason jail is appropriate in this case, at least partly because her partner bought a ticket to Mexico in January for her which was only cancelled after the government intervened.[1] Her counsel said it was in expectation of being found not guilty so she was able to attend a friend's wedding but the bummer for that theory is that it was a one-way ticket.
[1] https://www.nbcnews.com/business/business-news/elizabeth-hol...
What’s especially worth considering here is what Holmes did: most people expect high standards for medical ethics since lying as she did could have irreversible impacts on people’s lives. Her fraud involved inaccurately telling people that they had cancer, or giving values which lead to changes in medication or other treatments. That isn’t as bad as it could have been – I don’t believe anyone was given a false negative on cancer, for example - but it’s absolutely toxic for trust in the medical system if it’s not strictly punished.
Similarly, as a corporate officer she lied repeatedly to investors, regulators, and the public.
What both of those have in common is that they’re positions of trust where fraud is relatively hard to catch. Millions of people are in positions where they could on a daily basis abuse their customers’ trust and potentially never be caught, and so we have to consider the deterrent effect as well. Doctors, bankers, CEOs, etc. are highly paid so a financial deterrent isn’t nearly as effective at preventing lapses as the possibility of jail time - your family trust can’t serve it for you - and those consequences also mean that the people around you aren’t going to help cover it up the way they might if it was profitable enough to look the other way.
One can support reforms against punitive justice and still be disgusted by something like this, or one can also support prison reform while considering Holmes's crimes bad enough to merit a fairly strong degree of punishment in this specific case. Basically: complex subjects like this are full of nuance, and strawmen need not apply to and honest debate.
That's basic logic and fairness.
The two extremes are almost always both wrong.