Life is complicated, and people leave jobs all the time for reasons I expect you'd find valid (take care of an aging family member, move with your spouse to their new tenure-track position, ...).
Analogizing with another crime against a person's freedom to do as they please, consider "kidnapping." It includes forcibly restraining a person or moving them some place they'd like not to go, and in the eyes of the law the duration doesn't matter; people have unsuccessfully defended kidnapping charges for minutes of detainment. If you agree that the fees in question do rise to the level of indentured servitude (which seems plausible at least), then the fact that it's only for 4% of your working life shouldn't be a relevant consideration.