The GPL doesn't stop software developers from making money, only certain software developers that would like to market their software software in certain ways, like sell it as if it is a scarce commodity when it is not. Although I'll have to take his word for it, RMS is quick to point out that the vast majority of software is produced under private contracts or internally. Under these situations, the GPL has no "not getting paid" issues for developers as the software you produce under contract is the companies to distribute under the GPL or not distribute. In fact, the FSF has an explicit statement that NDAs for contracted GPL work are acceptable (https://www.gnu.org/licenses/gpl-faq.html#DevelopChangesUnde...). RMS doesn't have a problem with companies keeping their secrets or with developers not allowing you to see the source code they write so long as it isn't on your computer. The flip side is that he does have a problem with the independent developer that wants to write a closed source program and milk it for all it's worth by selling it by the copy or the subscription to end users. Admittedly this is a well represented group on Hacker News and amongst entrepreneurs in general, probably because copying bits can be a quick and/or easy way to make money when compared to getting paid for the actual development directly.
To his credit, RMS has been fairly clear (at least recently) that writing GPL software to sell copies is not a viable business model. And no, I don't think that developing proprietary software so that you can force a false scarcity should be called evil, but perhaps immoral is not too far off, and certainly sketchy.
edit: Actually, on second thought, I think RMS hasn't been clear on this; he seems to refuse to answer the question because it is irrelevant. If the business practice is immoral, it doesn't matter if it is viable. I took his silence as conceding the point.