There is a spectrum from those who have been lucky enough never to have paid a cent of real money, for example trained by a national carrier and repaying their training costs out of an excellent salary to at the other extreme people who have spent upwards of 100,000 euros in getting a licence and then pay another 50,000 to get a type rating with a few hundred hours on type.
If you think this is not safety relevant then we will have to agree to disagree. You are limiting your pool of trainees to those that can afford to pay. Airlines that use this business model (as you call it) have an incentive to churn their pilots so they can earn from the next trainees. So in the worst case they have a continuous turnover of inexperienced, unpaid temporary co-pilots. I see a very real increase in risk.
A decade ago there was outrage at the concept of bonding. But things have moved considerably further down the slippery slope. I think there are going to be accidents in Europe very similar to Colgan and I think the concept of corporate manslaughter will certainly be an issue for the managers responsible.