First though, credit where it is due: Seliger obviously thinks and cares deeply about this, and has much more real-world experience with it than I. (I am not a formally-trained educator; however I'm a good essay-writer when I put my mind to it, and have been drafted into teaching it on a handful of occasions). Furthermore, Seliger's description of the students he encounters -- their default writing habits and innate ability to explore unfamiliar knowledge domains -- rings absolutely true. He clearly knows what he is talking about in this regard.
However he goes astray in two key respects.
First, he gives examples of formal domains of knowledge ("Money", "Baseball", "Paul Graham's views on Entrepreneurialism") which are both full of abstractions and relatively disconnected from most kids' lives. It should be no surprise that they have difficulty engaging with these subjects in depth or with passion. But Seliger then goes on to conclude that therefore, his students lack the capacity to engage with real-world unbounded knowledge domains.
This is wrong, and it comes from looking at the problem through the wrong end of the telescope. Instead of saying "here is an interesting and well-written body of non-fiction essays about [ money | baseball | ... ]; let's see if I can get my students to engage with it," one should say "here is an issue that my students are engaged with; let's see if I can get them to engage with it as writers / essayists".
Most kids' lives are richer and more problematic than adults comprehend. This offers plenty of material to unpack and examine, and flex their cognitive muscles in the process. For example: where I live in London, we had a series of major youth riots earlier this year. (Well, major for the UK; having grown up in California, they honestly seemed quite tame to me.) Many highschool students participated in these riots, or had friends who did, or had homes / communities / favourite social spaces which were affected by the riots. Certainly ALL young people in London are now being directly affected by the collective response to the riots, on the part of politicians, police, educators, etc. I frequently hear young people espousing various opinions on the subject at bus stops -- rarely very nuanced opinion, mind you; mostly just expressions of the degree to which something or other is bullshit, but no matter -- and that's a good signal that it is something which is sufficiently part of their lives, and which they feel sufficiently passionate about, that it merits exploration with improved analytical techniques.
So if I were teaching essay-writing here in London, I'd start with the riots. I wouldn't even start with the the literary response to the riots -- that's already a bridge too far for most highschoolers -- I'd begin with the television reporting about the riots, and seeing what kind of response can be elicited from that. Having engaged their interest within a relatively familiar medium, I'd then move gradually into the more literary explorations of the domain: first to short opinion pieces written in the daily papers; then to longer analytical essays and parliamentary addresses; finally to the various explicitly literary / artistic means of engaging with the subject, such as the plays about the riots which are now beginning to emerge.
In other words: start with the passionately familiar, and figure out how to get from there to the literary. Not the reverse. If you think that your students have nothing that they are passionately familiar with, then look harder. They do.
The second place where Seliger goes awry is in ascribing value to the process of conducting literary analysis within an explicitly bounded domain (ie a single essay). I hold the somewhat unfashionable view that this violates the very point of education. In my opinion, the whole and entire point of education should be to prepare people to engage with unbounded domains of knowledge in a confident and competent manner. Anything which avoids the necessity of teaching students how to do this is counter-productive, at least in the real world.
An example: along the way to getting an architecture degree, I once took a graduate-level architectural criticism / philosophy course, taught by a professor who very much came out of the tradition of French post-modern literary analysis. When I attempted to critique architectural manifestos from the perspective of social / environmental / economic / psychological / cultural utility, she gave me the lowest grade which would let me pass the course. Why? Not because of the poor quality of my thought or writing -- that same year, I won the grand prize in a national essay-writing competition on the subject of "Architecture as a Social Art" -- but rather because I had committed the grievous sin of suggesting that there was some kind of external objective reality which in any way had something to do with architecture.
In her literary-criticism universe, any system of thought could only be legitimately judged with reference to itself: how internally consistent was it? What interesting implications could be derived from the self-interaction of its principles? In other words: take a domain of knowledge / body of literature, treat it as though it is fully bounded, and procede from there. Although I can see how this is a useful technique for academic literary analysis, I would submit that it is in fact incredibly HARMFUL for any domain of knowledge which directly interacts with the external real world (ie the unbounded world).
So that's my second critique: literary-criticism techniques are only really useful with respect to literary-criticism, and should be considered harmful with respect to most other domains of knowledge. Educator who default to these techniques because their bounded domains are easier to deal with are doing their students a fundamental disservice. Writing essays about unbounded domains may be harder and messier, but if you don't do that, you're not doing your job.