Many teachers object to Direct Instruction, though few verbalize what I think is the core reason as well as Marilyn Wilson of MSU. It's rather neatly summed up in a quote here:
Teachers no longer need to plan their reading curriculum or consider the variability of their learners; the script must be followed. "Scripted curriculum" says Linda Rice, "has the effect of deskilling teachers who become simple deliverers of content and skill processes rather than those who intricately synthesize content, skills, and concepts to create sophisticated curriculum designed to meet the needs of their particular students."
The "deskilling" is the perception teachers have of following a script. They want to feel that they themselves are determining the children's needs and responding to them. Following a script will, in their minds, make their role more menial, rote, and less "professional", and turns themselves and the children into "robots".
On the schools matter blog Jim Horn points to some Direct Instruction videos, claiming that they show a "neo-eugenics system of cognitive decapitation" (neo-eugenics? I tend to wonder why Horn sees fit to bring up suggestions of racism, which has nothing to do with either side of the debate. Perhaps for dramatic effect?). I'd encourage anyone to watch them. He doesn't mention the videos are of the Baltimore City Springs school, which had been one of the worst performing schools in Baltimore. It was an urban school, with all that implies: poverty, behavioral problems, etc. Within a few years, they were within the top quarter of schools in the city. Given this, does he really see a problem with a teacher bringing the children through a reading curriculum in which both the teacher and students interact, where the teacher gives praise in an appropriate manner, and the students are learning the fundamental skills exceptionally well?
What teachers would often prefer to do is what they have been doing: creating a lesson plan, day-by-day (or, using the lesson plan they've built over past years), and including a lot of fun activities, such as reading aloud to children. They don't tend to keep good data on results, and the normal human tendency is to think one's doing a reasonably good job. So, they think taking their hands out of the curriculum is "devaluing" them.
I feel their perception is unjustified. Many people find following the DI "script" difficult, and it takes quite a bit of skill and initial training to do well. The science of behavior is not as advanced physics or chemistry, perhaps, but it is nevertheless rigorous and precise. Despite this precision, students do not respond to behavioristic techniques as if they're being "mechanized"; they respond as if they're involved in learning. Moreover, many professions follow scripts as a matter of course: police officers are rigorously taught how to behave with suspects and victims, doctors follow scripts both in performing procedures and in giving medical advice, and pilots follow scripts for everything from routine takeoffs and landings to emergency procedures. No one allows these people to learn the practice of their professions solely through on-the-job experience.
A DI teacher needs to be on top of their game constantly, and following a DI curriculum is far more difficult than reading to kids (which any parent could do). The skillset of a professional teacher is not, and should not be, in picking textbooks that reflect their ideology or inventing a curriculum. It should be in teaching -- actually conveying information and skills. A teacher who can do that, rather than being deskilled, is highly skilled, and deserves to be termed a professional.