Expanding on my comment concerning the apparent source of absurdity in the Gentle Murder Paradox, I think that the apparent absurdity of the Gentle Muyrder Paradox arises from the transgressive behaviour premised in "you will kill someone", and that this is unavoidable. I'd argue that in this case, propositions have multidimensional value — social acceptability/transgressiveness, in addition to truth/falsehood (where "OBx" simply transforms the social value of x to a logical value regarding social normatives) — and that it also arises because there is a sense in which social obligations can hold with greater or lesser force.
I present an example below which more explicitly demonstrates these features of the Gentle Murder Paradox, in another context.
On factual detachment with socially transgressive well-formed formulae
It is not clear that there is more to Factual Detachment than modus ponens. Using the notation OBq ("we ought q") allows us to re-express the conditional OB(q/p) as (p ⇒ OBq) — which we would gloss equivalently as "if p, we ought q". Then factual detachment is simply
p , p⇒OBq
as a straightforward application of modus ponens.
Indeed, it is not clear that deontic detachment is any improvement in the case of the Gentle Murder paradox. If you forbid factual detachment, you can avoid deriving OBq from the premise p and OB(q/p), but one might argue that — in addition to being special pleading against modus ponens — this obscures the facts of the matter multimodal valuation of propositions, and the consequences of propositions which may be true, but are socially transgressive. If we consider the inference
OBp , OB(q/p)
then the only thing which differs here is that, in the case that p is "you will kill someone" and q is "you will kill someone gently", the absurd conclusion OBq follows from an absurd premise OBp. If we use factual detachment, then the fact that we obtain the false conclusion OBq is that, while p may or may not be absurd, it is socially transgressive — regardless of its positive or negative logical value, it has a negative social value. One can express this by OB¬p, perhaps, to reduce constructive behaviour to truth values; or one can see the Gentle Murder Paradox as hinting that in this system, well-formed formulae may be valued in a multidimensional way, where OB discards the logical value of a proposition and promotes the moral component to the place held by the logical value.
An example of a moral quandary from inconsistent obligations
This can be illustrated with a case where one has multiple, inconsistent, logical obligations. Suppose that
then we would normally say that OB¬p and OB¬q. However, there are some circumstances where telling people the truth would hurt other people's feelings: where ¬p⇒q. Consider
and suppose that q ⇒ (r v s). On the whole, we would tend to say OB¬r and OB¬s. However, given the choice, it is reasonable to suppose that it would be better to make them cry than to make them violent. That is: there is a sense in which OB¬r holds more force than OB¬s. This would suggest that OB(s/q). Suppose that you decide to tell someone a hard truth: then we have
¬p , ¬p⇒q , OB¬s , OB(s/q)
OB¬s & OBs
which is a moral absurdity which follows from the fact that telling a hard truth is socially transgressive, and that while making someone cry is not a good course of action, it is a better choice of action than the other possible consequences of telling a hard truth.
Indeed, the crux of the paradox here is that the triad of OB¬p, OB¬q, and ¬p⇒q form a moral dilemma. If ¬p, we obtain (q & OB¬q), which, while not a contradiction, is an expression of a violation of one's social obligations. The alternative in this case is to choose ¬q, in which case we may derive (p & OB¬p); which is also a violation of obligations. This is the same as the transgression (p & OB¬p) in the Gentle Murder paradox.
In any case, the issue here seems entirely to be based upon a socially transgressive premise, from which one can derive a formula of the form (p & OB¬p); and that there are different strengths of obligation, so that some moral absurdities (you should make someone cry, you should kill someone gently) are less terrible than others (you should make someone angry and violent, you should kill someone brutally).