I think it's worth contemplating tenured prof. Tyler Cowen's thought experiment in response to the article.
Take a 53-year-old professor, at a moderate quality university, who goes from publishing three articles a year to one article a year, and in somewhat lesser journals than before. His teaching evaluations slip steadily, though he never becomes a disaster in the classroom. In the no-tenure world, does that person get fired?
Looking at Cowen's CV, that might be close to the truth on the research side for him, although his CV also reveals he's a few years younger. I don't know about the teaching side. What it misses is that Cowen has produced a textbook and I think some decent selling books, plus a really well read blog.
Most of the public intellectuals in economics (Cowen, Mankiw, Krugman, DeLong, Becker, Levitt ect.) have tenure. It could be that tenure professors have more experience so are better writers and have gained a larger audience.
But I think back to the two stars of the year I was on the job market: Emily Oster and Jesse Shapario. When they were on the job market they were in quite a few articles and seemed to try to participate more in the public discourse. But I haven't heard much from either of them lately except press releases of their research. My guess is that they are working as hard as they can to get tenure by publishing articles. In a few years I wouldn't be suprised to see them more in the public discourse.
Without tenure the people I've named would still be at top schools. But professors at smaller schools make contributions at a more local level in OP-EDs and speaking to local groups.
I see the obvious arguments that some professors with tenure will slack off and not be very productive. But I think without tenure many professors would decrease their contribution to the public discourse.
From a personal standpoint, I don't have tenure. I'm not sure how my effort in research, teaching, and blogging will change once I get it. My guess is not very much, but I hope I get to make that choice.