Everybody who seeks to make a profit has a mixture of inputs to their operation. You need a mix of skills, tools, and materials. The exact mix chosen depends on the price and value of those things. A radical change in the price of any one component will make the current mix double-plus ungood (thank you, Don Lancaster). The proportions of the mix will change, with more of the cheaper input being used.
In other words, free software means that the efficiency of the IT industry has greatly increased. IT products have become cheaper. This will result in MORE total IT spending. More programmers will be needed in the future, not less. RMS got the economics completely wrong in his manifesto. We recently had a discussion about economics that ended up in me purchasing him a copy of Economics in One Lesson.