Barry asks, "I don't think we can easily say that they had a certain strategy of attack on scripture. Doesn't this input motive?"

No. It doesn't. Every argument takes a form (or "strategy") to get to it's conclusion. Recognizing or unveiling the form has nothing to do with imputing motive.

If someone says, "Socrates claims to be mortal but he is clearly not:

P1: All men are mortal.
P2: Socrates is a man.
C: Socrates is a mortal.

And another person looks at the above argument and says "The person is using deductive reasoning in order to negate Socrates' claim to immortality" this is not an observation as to the motive of the person presenting said argument, at least not in the sense which you or Bock refers to. That would require the person to explain *why* they are presenting the argument in that form or some other such observation.

Furthermore, figuring out a person's motive is not always a bad thing. Sometimes, it is a necessary thing.

Lastly, Lisa Miller has stated her motive. Cf. NPR interview with Al Mohler and Miller (you can find the link at Mohler's blog).