I have no data, I'm simply stating my beliefs to give you an understanding, since I feel I'm one of the people you happen to be surprised about.
Free education levels the playing field. Moreover, I feel guilt. I have been a beneficiary of free education. Free transport, free college tuition, free books and some paid assistance with living somewhere else. Coming from a working class family it has given me an amazing boost in:
* Career (master computer science)
* Spiritual knowledge (one Buddhism course was enough)
* Outlook on the world
* Network
University isn't perfect, but if I wasn't given this chance then I would not be able to replicate certain pivotal experiences simply by using the internet and my own wit. In that sense, I still believe it levels the playing field by quite a bit.
School was always meant as the great equalizer and I think it still should be, as imperfect as it is.