While I certainly appreciate the skills gained from a background of climbing the GA -> TP -> Jet ladder, for many of us in Europe it just isn't an option any more due to financial constraints and the general lack of GA flying. I went through a cadet programme and started on the A320 with about 250hrs, if it wasn't for the semi-sponsored scheme I would never have been able to get where I am today.
With the right combination of good training, experienced captains to learn from and the right amount of humility/willingness to learn there is no problem with having cadets as part of a balanced intake to an airline. The problems start when cadets make up the entirety of the job market as is currently happening with CTC and Oxford in the U.K. This makes it difficult for self-improvers and tends to depress Ts and Cs along with general experience levels in the flight deck.