There's almost nothing that advocates won't say about open source - here's a good example of the triumphal school of thought:

So, for example, I take it for granted that open source will be as successful on the desktop as it has on the server - with the caveat that the desktop itself may well be far less important in ten years' time. I also assume that everyone will be using ODF as the standard for document interchange and storage, and that GNU/Linux will consolidate its growing success in the field of embedded systems.

The question you have to look at is this: which open source projects have succeeded in a large way without major corporate funding? That's suddenly a thin list, isn't it? Here's another thought: had Microsoft released Visual Studio as free software 10 years ago, that almost certainly would have been seen as predatory behavior. IBM released Eclipse for free, and it's killed off all the commercial Java IDEs out there. Sure, the source is available - but why isn't that seen as predatory? The net effect has been the same.

I'm not nearly as cheerful about OSS as I used to be, and it's due to the fact that OSS in the hands of large companies is a "get out of jail free" card for what would otherwise be seen as predatory behavior.