According to the Christian tradition, sexual activity is impermissible unless engaged with procreation or union as a goal (the latter is variously understood, and "union" isn't always the best word). So just as deontology recognizes actions that may not be done for any end whatsoever, the mala in se, we can also introduce a category of "obligatorily directional action". A type T of obligatorily directional action comes with a set G of goals such that (a) G is a non-empty proper subset of the set of all goals permissible to human beings, (b) G is not defined solely in terms of the amount of value embodied by the goals in G, and (c) an action of type T is impermissible unless it is done with the intention (and not just foresight) of achieving at least one of the goals in G. I don't quite know how to put condition (b). I want to rule out such cases as this. Causing a minor pain can only be done for the sake of a greater good, so if we didn't require (b), we could let G be all goods greater than a minor pain, then any action type that entailed a bad of some paticular sort would count as obligatorily directional. I shall say that G is the set of T's proper goals.
The mala in se are a degenerate case where the set G is empty. The plausibility of the claim that there are mala in se makes it necessary to take seriously (apart from particular claims from the Christian tradition) the possibility that there could be obligatorily directional actions.
I can imagine two kinds of obligatorily directional actions, which I will name the suspicious and the sacred (without that implying any theological content; think of fairly secular uses like "sacred duty"). A suspicious obligatorily directional action is one that carries in itself some innate reason to think it is morally problematic, but that problem disappears when, but only when, the action is done for a goal in G. A sacred obligatorily directional action is one that it would in some way be in some sense (perhaps a fairly secular one) sacrilegious to do except at least in part in pursuit of a particular goal. One might, for instance, think that intentional killing is a suspicious action, and is only permitted when done at least in part as a just punishment or as a defense of the innocent against a wrongful aggressor—then G would include the goals of just punishment and defense of the innocent. On the other hand, one might think that prayer to God is a sacred obligatorily directional action, and that it is wrong to pray except with some sort of communion with God being a goal. Thus, it would be wrong to pray solely because someone will pay us to do so. Indeed, Catholic tradition condemns as a sin someone's attending Mass (solely?) for the sake of secular benefits.
I do not know if the sacred and the suspicious cover all the cases. For instance, I've been drawn to the view that when asserting one is obliged to have the intention of asserting nothing false. I don't think asserting is suspicious. And I don't know that I'd say it's sacred. On the other hand, maybe given that the second person of the Trinity is the Word, it is?
At times, there can be disagreement over whether an action's status as obligatorily directional is because it is suspicious or sacred. Thus, I suspect that many Catholics in the past thought that sexual activity is obligatorily directional because it is suspicious, while the more common current view is that it is because it is sacred. Actually, it could even be that an action is both suspicious and sacred. The sacred is often dangerous, after all.
Note that to every obligatorily directional action type there correspond an infinity of action types of mala in se. For if T is obligatorily directional with proper goals G, then for any g not in G, the type an action of type T done solely for g is a malum in se.
I think the concept of obligatorily directional actions needs more investigation.