As someone who has gone 'management - flight crew - management' I empathise with the bad feeling with regard to bonds...however from the management side you must underside that the airline is investing 'real money' in the initial training of a flight crew member and as such needs some form of 'comfort' in that investment...in my opinion we would be negligent in our duty to the shareholders/investors/other staff members if we did not secure this (I do not agree with existing crew being 're-bonded' for a new type however)...
This situation is not unique to aviation and I see/hear of many similar situations in diverse industries, IT..electronics etc., whereby staff have key training/qualifications provided by the company and are contracted accordingly...in many cases far more tightly than with most airlines!