Bhante, I have not had the time to read all of the 115 posts in this thread, but I have seen the following point mentioned in one of them, although not addressed directly to the discussion about “thorns”, so I thought I would chip in my 2 cents.
Here is a quote from AN 9.41:
"So at a later time, having seen the drawback of directed thought, I pursued that theme; having understood the reward of being without directed thought, I familiarized myself with it. My heart leaped up at being without directed thought, grew confident, steadfast, & firm, seeing it as peace. With the stilling of directed thoughts & evaluations, I entered & remained in the second jhana: rapture & pleasure born of composure, unification of awareness free from directed thought & evaluation — internal assurance.
"As I remained there, I was beset with attention to perceptions dealing with directed thought. That was an affliction for me. Just as pain arises as an affliction for a healthy person, even so the attention to perceptions dealing with directed thought that beset me was an affliction for me.
It seems that the expression “I was beset with attention to perceptions dealing with directed thought”, which describes vitakka as “an affliction” just like “pain arises as an affliction in a healthy person” corresponds quite closely to the concept of “a thorn”.
So if we interpret the “thorn” in AN 10.72 as meaning the “affliction” that represent “attention to perceptions dealing with directed thought” (vitakka-sahagatā saññā-manasikārā), then the thorn simile is consistent throughout AN 10.72 in the understanding that it represents “something that creates difficulties for what it touches” rather than “something that cannot be present without destroying what it pierces”, since in AN 9.41, “attention to perceptions dealing with directed thought” do not “destroy” the first jhana but bring some kind of “pain” into it, arguably like a thorn.
It would be consistent with “seclusion/company”, “developing the sign of loathsomeness/an agreeable sign”, being “protected in the mental faculties/sight seeing”, “leading a celebate life/the behavior of a woman”. For each jhana, an interpretation along the lines of AN 9.41 would continue with a consistent image of “thorn” mirroring “affliction” or “pain”, while not “destroying” the state it afflicts. This understanding is also supported by the last three items:
"Greed is a thorn. Hate is a thorn and delusion is a thorn.
Here thorn is also quite clearly understandable as “affliction” or “pain”.
So AT may have expressed himself in a dubious manner at some points, but there is an understanding that seems to be consistent with the suttas and with the general arguments he makes regarding the interpretation of AN 10.72.
Or am I being wrong?