And in blue cities, increasingly they're not held for trial. So they go out and reoffend.

Yes - because you can't just be "held for trial." Because that's being "imprisoned without conviction." If you haven't been convicted of a crime, you can't have a punishment imposed (being locked in a jail) before the trial.

There are exceptions. If prosecutors can demonstrate that you're a flight risk, they can take measures that will ensure that you will show up when required. Only in certain, very specific instances will those measures include pretrial detention - usually you can avoid pre-trial detention by posting bail, and you have a constitutional right that such bail not be "excessive."

Again, this is an essential and unavoidable consequence of personal liberty. Perhaps the most significant state power is the ability to incarcerate you. For all the concern about deprivations of personal liberty that get discussed at length in political conversations, virtually no action by the State results in a greater loss of more liberties than being imprisoned. So you have rights against the state to keep them from being able to imprison you without a trial - which includes not being imprisoned for the time between being accused of a crime and the trial on that accusation.

Albaby