Prefixes are necessary, for exactly the reasons Eric states. I'm surprised there is any controversy over this at all. Even today many of the prefixed styles have browser syntax differences that have to be resolved before they can become unprefixed standard properties.
But you have to write the same rule four times? Well boo hoo. That's the price of using a feature before it is standardised. If you don't like it, just wait and you won't have to do it in future.
If we got rid of the prefixes, we'd end up with all the CSS compatibility nightmares and hacks of the past. That's not worth it just to make your life as a web author marginally less copy-and-pastey.
The problem with the prefixes is not the prefixes. The problem is that the CSS specs are developed too slowly. box-sizing, for example, has been a done deal for many years, but since the CSS3 Basic User Interface Module has stalled at Candidate Recommendation stage we are still unnecessarily typing -moz-box-sizing.
That's a failure of process on W3's part, not a technical issue to do with prefixes. CSS3-UI needs to be finished and a full Rec. If CSS3-UI cannot go forward due to technical reasons in another part of it, those features either need to be killed and scheduled for CSS4, or the module needs to be split/reorganised so that the stable bits can go through.
Arguably the whole Module system is not granular enough and needs to be split into one-standardisable-document-per-feature. There is a lot of stuff in CSS3-UI which has no impact on box-sizing or outline features. We shouldn't be waiting on that stuff to standardise the uncontroversial features.