I think that paying back would a way to go out of this system. But the loser will be the tax payer. When the state/politics decided to give licences for free (a long time ago) and then let the offer and the demand decide the price, they created a speculative bubble: every buyer expected to resell it for at least the same price or make a profit (often a big one). Now, if this market is opened to more actors, the lasts to buy will get a big debt out of their deal and may be in a bad position for the rest of their life.
For me the ones to blame are those politics who created this situation. Concerning the taxi drivers who made a big profit, why should they be blamed for a system the state has put in place? (well, I do for being so greedy and making the taxi a transportation for affluent people)
Note also that taxi drivers are well known for hidding parts of their revenues (proof or source: none). Because of that, taking the taxi is really the last resort for me.