I think the wording is reasonably clear, and you are misreading it. "I disagree" alone tells us little, but all of the support below seems to serve much more strongly to justify disagreement with "you should know ..." than with "IQ ..."
No, actually, below the ambiguous "I disagree", we find "I've never used my IQ as justification for anything, granted, but I had no idea it wasn't considered a solid measurement." That seems clearly to point to a disagreement with the presumed objectivity of IQ testing, not its application to the OP.
Well, apparently it is not clear, because it seems "clearly" to me to mean the other. You are taking "I had no idea that X" to be a claim of "not X"; I think it is a claim that they had no idea that X - and the pragmatic purpose of this in the conversation was "... and therefore, I don't think having no idea is crazy". I think your interpretation in this context is - at least - uncharitable.
> Well, apparently it is not clear, because it seems "clearly" to me to mean the other.
Let's look at the original exchange. The person to whom I replied said, "I've never used my IQ as justification for anything, granted, but I had no idea it wasn't considered a solid measurement."
I replied, "It isn't remotely a "solid measurement", in fact it's a field surrounded by justified controversy on multiple grounds" ... and more in this vein.
How is that in any way ambiguous? It's a discussion of the credibility of IQ testing.
> I think your interpretation in this context is - at least - uncharitable.
My interpretation is based solely on the words used in the exchange. Charity has no role.
Again, "I had no idea it wasn't considered a solid measurement" does not mean "I am asserting it is a solid measurement". It is quite obviously not the same statement (use of the past tense, for one - they make no claim about what ideas they have now), "from the words in the exchange". It is true that sometimes "I had no idea that X" is used to mean "I don't believe you that X." It is also frequently used sarcastically to mean "obviously X". But from context, I think the statement was quite literally a statement that they had no idea. This was relevant because, again, you had just asserted to someone else that it was unreasonable to have no idea.
Lastly, charity has a role in any conversation - particularly those involving disagreement. If your conversation partner might be saying something stupid or something reasonable, taking the reasonable interpretation or checking what they meant produces better conversation. I myself would sometimes do well to remember that, in the heat of discussion.
You are not being ambiguous. The poster who replied to you did not want to engage in an exchange with you, so he retreated from it - thus his use of the past tense "had" in reference to his prior belief. Given that every argument he provided referred to his not caring about the importance of whether IQ matters, I think this is the only reasonable way to read his post.
