Let's put the "those who can't do, review" idea to rest
Over the years, reviewing theater at all levels, I have encountered the oft-repeated mantra that "those who can't do, review." Rarely invoked by an individual responding to a review with which they've agreed, it has a way of dismissing the reviewer's opinion by implying that he or she doesn't really know what they're talking about. In my experience, though it happens, this is rarely the case, and I always find the quote to be offensive.
You can't really alter the quick rhyme to reflect the reality, which is somewhere between "those who can't do, occasionally review," and "those who review, sometimes don't know what they're talking about." No fun in that phrasing at all.
Is it necessary for a person reviewing a theatrical production to have actually participated in the creation of a production in some capacity or another, in order to validate the expressed opinion? I think not, because an understanding of the difference between an effective and ineffective production is attainable without recourse to actually having done such work. In much the same way, you don't need to be a singer to hear when a vocalist goes off-key, nor does the fact that you "can't do" invalidate your opinion of that off-key moment.
Theatrical productions, of course, are much more complex organisms than a rudimentary musical scale, in any key. Understanding what makes a given production work or not work is not necessarily as instinctive as the perception of a single sour note. Thus, while it may not be necessary "to do" (or have done) the actual work, it's critical that a reviewer understand not only his/her instinctive reaction to a production, but how to translate that reaction into language that a reader can understand.
You can't just call an actor's performance ineffective, because in and of itself, that word doesn't say a lot. Why was it ineffective? What could or should have been done to make it effective? That information is important to both an uninvolved-with-the-production reader, as well as the performer, and others involved with the production, most significantly, the director, for example.
To my knowledge, Frank Rich, once known as "The Butcher of Broadway," was never involved in a theatrical production, prior to his run as theater critic for the New York Times (1980 to 2011). As far as I know, he was never a politician either, before then becoming an op-ed columnist for The Times. Though often inclined to cringe at the bluntness and arguable cruelty of his style, I've never had cause to doubt his understanding of theater or politics, regardless of whether or not I agreed with an opinion of his on either subject. I'm fairly certain that given his keen insights into a variety of productions, as well as motivation and opportunity, Frank Rich could do theater work; maybe not design and/or operate lights, or head up the costume department, but certainly produce and/or direct. Though not strictly speaking 'theater,' you might count his role as one of the executive producers of HBO's Veep as evidence of this. So, in his case, the idea that "those who can't do, review" does not really apply.
Whether you're discussing Broadway, regional or community theater, reviews are inevitably local in nature; about local productions, written by local employees, employed by local publications. In New York, of course, there are numerous examples of each of these local components, a great many of them, professional. Paducah, Kentucky (random example) is a different story, where a recent production of Mary Poppins by the Market House (community) Theater was reviewed in The Paducah Sun.
Particularly at the community theater level, it's hard to criticize a reviewer for his or her presumed inability to do the work, when to do that work, locally, could create a potential conflict of interest. I was acutely aware of this potential for conflict of interest during my tenure as a theater reviewer for The Patriot Ledger, a daily newspaper in Quincy, Massachusetts. In this capacity, I was often asked to review productions of nearby community theaters (Braintree's Curtain Call Theater, or Hingham's Civic Music Theater) for whom I was often working, as either an unpaid performer, or paid director. As long as I had not auditioned or was, in any way, involved with a given production, they'd give me the assignment, which would often put me in the position of reviewing people I knew personally. Though not in all cases, my reviews were generally respected by members of these theatrical communities precisely because my ability "to do" was a credential for the review itself. Not that this successfully curtailed all criticism of my written work (it didn't), but differences of opinion were often spoken of frankly, and allowed to stand on a rational agreement-to-disagree basis.
As a director, I was often on the other side of this equation, too, and knowing me certainly never seemed to inhibit other Patriot Ledger reviewers from criticizing my theater work as actor or director when they felt it to be appropriate. In fact, one reviewer and I went head-to-head in a series of back and forth words, published in the Patriot Ledger, following a review of Jesus Christ Superstar, that I had directed for a Quincy church group.
The point of all this is to question the validity and usefulness of the "those who can't do, review" idea. While it may certainly be true on occasion, it is not true often enough to warrant its elevation to an established fact. And certainly not true often enough to make its articulation an excuse for shoddy theatrical work.