Free Open Source Kills Markets. [Don Park's Blog]
I agree with this up to a point. Open source will put crappy commercial software vendors out of business and kill the market for basic infrastructure code like XML parsers and DOM implementations. However I don't think people should have to pay for those kinds of things anyway.
My take on it is that open source is great for reusable infrastructure and tools and helps to raise the bar of software. Companies that embrace the best open source technologies around will be able to build better quality software, faster so they'll be able to do more and build more powerful software.
Open source promotes open reuse in the software industry rather than us all having to reimplement the same stuff again and again, reinventing wheels. I don't think anyone should need to buy a DOM implementation, to quote Don's example :-). Indeed sharing things like DOM implementations in open source allows us as an industry to pool our resources together to build a great (say) DOM implementation, share it amonst ourselves then then use it to build better software that solves real business problems. (or you could try dom4j instead :-).
Rather than killing markets, I see it more as focussing markets to provide real value to customers, rather than trying to sell a small piece of code like a DOM implementation that should be shared across corporate boundaries. So it focusses companies into building real solutions to business problems built on top of open source.