Fare jumpers absolutely need jail - the sort of person who jumps the faregate is also much more likely than the average person to be a nuisance or a violent threat to other people on public transit. I think it's more important to jail fare jumpers than a lot of other types of petty criminal, because enclosed public transit is one of the most important areas in a city to control crime; people need to feel safe on public transit in order to want to use it to get around. The sort of person who fare-jumps is extremely often homeless, mentally-ill, or a gang member - not someone who is capable of being compelled to do a minor chore for the station without way more coercive effort than the station employees can be expected to provide. The right response to fare-jumpers is to have police - uniformed specialists in using violence or the threat of violence to enforce public order - physically remove them from the public transit station and keep them in a locked room under guard where they can't harm someone else.