> arresting someone doesn't mean that they are guilty, so why out them
Indeed, they are not guilty and the problem lies with the assumption that they must be guilty because they were arrested. It being a matter of public record that (and where/when/why) they were arrested means their loved ones can know what happened to them when they don't come home (even if that means they have to find the answer themselves, though ideally they wouldn't).
Just consider someone very close to you is arrested but there is no public record of that arrest for you to follow up on. What do you do?