I am divided. As a developer, I think open source is great. As an entrepreneur, having more people release stuff for free devalues my work on the long term. I would say a good middle ground would be that open source should only be used to provide tools to developers, not to release production features.
A few years back, people would buy a software $25, now they complain when your app is over $1 (thanks Apple).
The dream is that we can keep climbing the ladder of abstraction forever and build more complex software (and presumably sell it), by assembling the free and open-source software. Climb a rung, repeat.
The problem is we are bounded by our imagination and hardware. So we just keep making the same stuff in 100 different ways.
In a world where developers at places like Amazon have been putting huge numbers of people out of work, and the tech industry cheers this as high-value disruption of moribund industries, developers who think they should be immune to the same forces are breathtaking in their arrogance.
If you can't compete you lose. If someone can do it for free rethink your business model.
Why should people not release things simply because other people are unable to compete?
Plus, both of these rely on the free (as in beer) service twitter. twitter has been copied several times (app.net, rstat.us , identi.ca) yet it is still the power house.
Don't fall into the same trap as the recording industries did, which is to assume that your market model will stay the same for ever. It won't, and developers don't tend to have the same lobbying power to get new laws to try and cling onto their old model.
Go with the flow and find other ways to monetize your skills.
This makes for a decent developer analogy for the arguments designers have about services that devalue their time and efforts too. I don't know where the middle ground would be for us, though.
FOSS is a wonder of the world. The idea that we can all run this stuff, read the source, and make changes is incredible. There is still plenty of opportunity to make money as a developer. If you have any skill at all, you should not feel threatened by a tweet scheduling app. And there's still software at $25 and up, even in the App Store. Just aim at a market that will pay for quality apps.
Meh, I can do the same thing and undercut you on price, or offer a "better" freemium model. If being unique is your competitive advantage, enjoy your very brief time in the lime light.
A few years back, people would buy a software $25, now they complain when your app is over $1 (thanks Apple).