Ok, so I'm starting to get the sense (I'm sure you are too) that some of the points are cycling back on themselves in separate paragraphs. Given that this is a discussion over days with context switches in between, it can become easy to lose the sense of direction (I blame myself for this). So, I've gone ahead replied below as I would anyway, but it my argument might make more sense if I summarize it here, and then consult the fleshing out below to address concerns. Nonetheless, I will still respond to either section, I just thought this might simplify things :).
To summarize my stance: 1) At their core, ALL decisions are the inescapable direct result of a net-weight of fulfillment of desires. To disprove this, all one need do is provide a decision (conscious or no) made completely devoid of fulfillment of desire (ie., self-interest). Since I consider such a task impossible, by contradiction I must assume that 1 is true.
2) Amongst the myriad desires humanity holds, reason is a common resident. (Most people desire to be reasonable).
2a) Reason is an effective tool for optimizing self-interest. Consider the counter position. Should a person behave unreasonably, they intentionally neglect to observe and temper certain desires over another. Therefore, their interests are dependent on a system that cannot assess whether it is truly maximal, and thus by probability run the likelihood of not optimizing self-interest--and should they do so, would be completely unaware that this is the case.
3) If people are reasonable, then they maintain assessments of the world (ie., beliefs). Since these beliefs are a result of reason, they are directly related
4) Should a person desire to be reasonable, then by 1) 2) and 3) decisions are inherently also weighed by one's beliefs and reason.
5) The is-ought argument is the observation that factual statements cannot produce "ought" like statements, wherein "ought" is appealing to some authority other than the observation itself. "Ought" statements in regards to mathematics, for instance, are not problematic because they are a consequential observation.
6) Making "ought" statements with respect to desire/self-interest do not succumb to the is-ought fallacy because they are consequential oughts derived from reason. Suppose I say, "one ought to be reasonable," or in other words, "one ought to weigh considerably the desire to be reasonable." Given by 1) that decisions will be influenced by desire regardless of whether or not a person is aware that such is the case, and 2a) that reason is an effective tool for optimizing self-interest, then the statement is a logical consequence of recognizing driving force and end goal. It is no less objective than saying "one ought to measure ingredients when cooking" or "one ought to apply the principles of algebra to achieve an accurate solution."
By contradiction, should I say "one ought to be reasonable" with respect to something else (anything else) I inescapably encounter the is-ought problem. For instance, saying "one ought to use reasonable" because it is "good" or because "God asks us to be" or because "we should know the truth" these all apply appeals to the desire itself and not the fact of the decision making process.
7) Thus because all other appeals are guilty of is-ought, it is reasonable by 6) to conclude that 1) is the only legitimate appeal when making "ought" statements in higher level tiers of moral discussion.
I need to break this into separate parts, so follow up coming soon.