For one, she seems concerned for the well-being of the many struggling young academics who do not make tenure:
They've invested their whole youth, and are back on the job market near entry level at an age when most of their peers have spent ten years building up marketable skills. Many of them will have seen relationships ripped apart by the difficulties of finding not one, but two tenure-track jobs in the same area. Others will have invested their early thirties in a college town with no other industry, forcing them to move elsewhere to restart both their careers and their social lives. Or perhaps they string along adjuncting at near-poverty wages, unable to quite leave the academy that has abused them for so long.Honestly, I have no idea how many people this describes. Many who are denied tenure at one school go on to receive it somewhere else. But yes, there are certainly some academics who are functionally disbarred as a result of a tenure committee's decision.
What would happen if tenure were abolished? Would that ensure that these folks who try the academic career only to get drummed out of it could somehow keep their jobs? No, of course not. It just means that the one big veto point in an academic's career -- the tenure vote, which occurs usually 5 to 7 years into the job -- is spread out over a wider range of years. A school might fire an underperforming professor in her third year or in her tenth. And that person would still face the fate of trying to start over somewhere else. So McArdle's concern for the plight of the denied tenure applicant is noted, but it would hardly be ameliorated by abolishing tenure.
McArdle also goes after the whole idea that tenure protects academic freedom:
Most scholars in their sixties are not producing path-breaking new research, but they are precisely the people that tenure protects. Scholars in their twenties and thirties, on the other hand, have no academic freedom at all. Indeed, because tenure raises the stakes so high, the vetting of future employees is much more careful--and the candidates, who know this, are almost certainly more careful than they would be if they were on more ordinary employment contracts.Again, what would happen if tenure were abolished? Scholars would still be careful, because they could still be fired. At least in McArdle's framework, that caution would just extend until later in life. However, it's my impression that, to the extent scholars refrain from writing up truly radical ideas, they do so not to suck up to their tenure committee, but to improve their chances of publication. The biggest hurdle in gaining tenure is usually not teaching sufficiently well nor earning the respect and friendship of more senior colleagues. It's amassing a publication record. One does this by submitting manuscripts to academic journals, most of which utilize anonymous peer review. It's the peer review process that quashes most radical ideas, and really, most of them deserve to be quashed.
Now, of course, there are radical ideas and there are radical ideas. Some might perceive it as radical for a political scientist to suggest that legislative parties have no power to influence congressional votes. However, when this argument was crafted well and supported by compelling evidence and innovative methods, it got published, and its provocative nature encouraged further publications and a fascinating debate. On the other hand, if a political scientist writes 25 pages insisting that the nation that controls magnesium controls the universe and offers little in the way of theory or evidence, that paper will go unpublished, and its author, unless he can think up something else to say, will go untenured.
Even if tenure were abolished, young scholars would still be generally averse to associating themselves with discredited ideas. That's true of pretty much every profession. To the extent that a publication record were still necessary for promotions, salary increases, transfers to better schools, etc., scholars would still be interested in crafting arguments that their peers find credible. So yes, the discipline has a built-in resistance to outlandish ideas. And maybe, in some cases, that's regrettable, quashing ideas that really should be out there. But I still fail to see how abolishing tenure solves this problem.