It down to what you sign up for in the first place, don't sign and then moan, there were quite a few baby guys who didn't like what was on offer and went else where, equally a good few turned down other operators offers so they could stay in the UK with a promise of the Midlands when able.
Most companies bond for training which is fair, some have started to push it a bit further to lock you in. Very few companies now care whether you've walked away from a bond if you can show your previous employer was a ball & chain company.
Its very simple, if you don't want people to leave treat them fairly and with respect, yes a few will always take the piss, but better to show the rest of your employee's that it is their ex mates that are taking the piss rather than the company taking the piss!!
The baby pilots who joined Norwegian were not bonded for the NG conversion, were paid full basic salary after completion of 2 week ground school course (daily rate during ground school including HTL) and full salary including allowances from start of production i.e. line training all are on a 1 months notice contract and two have left after a very short time and i understand the company was very grown up about it, basically if for what ever reason your not happy they'd rather let you go and they were paid every last penny owed, both parties move on and no incrimination or negative comment on forums such as this, all rather grown up.