But much of it is quite beneficial to both parties. My sister was debt bonded for a while; Crossfit paid for her personal trainer certification, but she had to pay them back if she quit her job in a year. A girl I dated is getting a Masters from Columbia, but she has to continue working for the Diplomatic Corps in her country for 3 years after graduation. In fact, many valley engineers meet the definition of bonded labor: you need to give back the signing bonus if you quit in < 1 year.
Economically, bonded labor with transparent contracts is a way to allow employers to pay to improve the human capital of their workers. On HN we often lament the fact that employers don't invest in employees, and the main reason for this is that they can't recoup their costs if the employee leaves.
In India and the US there is a lot of bonded labor and it ranges across the spectrum. Quite a bit of it - particularly among professionals - is not remotely exploitative and is economically beneficial. An informed discussion should acknowledge this.