Bonding by will or by force?

In my industry there was a severe imbalance among supply and demand of labour. The industry was growing in a much faster pace than the labour force it can attract towards it. This gave the employees certain leverage in dictating terms. During my tenure i was constantly being offered jobs from various foreign companies with higher pay grade and better ships, which leads to better working environment.
Most of the companies, exception of a few, hired the floating staff on a contract basis. It was a certain period contract which upon completion of the stipulated time invalid. So bond was not implemented on them. Only those firms which gave a permanent employee status imposed a bond.
When I joined my firm, i was asked to sign a bond of Rs 25,000 for a period of four of service. This was approximately one-third of monthly salary. When i inquired about the reason of such an amount being imposed, the answer was “What is the point?”. From the past experience the firm has seen that imposing a higher amount for a shorter period would lead to lower attrition rate during that period only and after completion the employees usually left because they felt the firm had hard restrictions on them (worked as negative psychological barrier). A higher period and amount lead to lesser amount of entries. A lower amount and shorter period did not serve any purpose. But a lower amount coupled with higher period did not have any psychological effect and in fact gave the firm an advantage over its competitors.
I, in general, feel that bond is yet another form of restriction put upon an already heavily burdened employee. The firms should really focus upon how make work more enjoyable and competitive at the same time so that the employee enjoys his/her work and stays with his own consent and rather not because of any restrictions. If any employee has really made up his/her mind to leave then staying will not help the firm in any way. The employee will not perform in his/her full capacity and rather becomes a liability to the company. The firm then should be happy to let go of those and make way for new entrants, who will really serve them properly.