First, we'll start with some definitions, which will help us to elucidate some possible objections to this argument.
- I will consider an action to be "objectively moral" if it is indeed moral independently of anyone's opinions on the morality of the action. I choose this definition because... well, it's what I understand "objectively moral" to mean.
- For "ought," let's look at some normal-person dictionaries, because, as I said in the comments, I'm no philosopher. Merriam-Webster says that "ought" is "used to express obligation". Oxford Advanced Learner's Dictionary says that "ought" is "used to say what is the right thing to do." These are slightly different definitions, but for the purposes of steelmanning this argument, we'll consider both the case where saying, "You ought do X," is equivalent to saying, "X is an objectively moral action," as well as the case where, "You ought do X," is equivalent to saying, "You are obligated to do X." I choose to separate it like this because out like this because, since this argument bakes a concrete definition of morality into (5), it seems that it assumes that morality does not necessarily imply obligation. (I am inclined to say that morality does necessarily imply obligation, which would be another potential objection, but I'll leave that aside.)
With that, let's look at each step of the argument.
- By definition a rational agent is, when exercising their agency, evaluating different courses of action before deciding among them. The actions they take are the ones that, in the moment, they evaluate as best.
- Define “happiness” as the mental state which this process brings about in the agent.
These are just definitions. There's no room for objections here. However, with respect to (2), I would note that there is some ambiguity in the statement as written. Is "happiness" being defined as the mental state brought about by the process of selection, or the process of selection paired with actually taking the presumably best action? This won't affect my analysis, but I figured it may be worth pointing out.
- Then happiness is intrinsically involved in your agency as the state of affairs your decisions are directed towards. Thus, you necessarily value happiness.
This conclusion makes some assumptions about "you" that are not supported in the argument as written. Since we are reaching (3) by applying (1) and (2), this line of reasoning requires us to accept that you are indeed a rational agent; if you are not a rational agent, then you do not necessarily value happiness. I'll speak for myself: I know for certain that I have taken actions that I have evaluated in the moment to be suboptimal, but still took those actions for reasons of self-preservation, self-promotion, etc. (Ironically, I would call those of my past actions objectively immoral 😉, but that's beside the point.) But even if we can confirm for certain that you are a rational agent...
- Thus you ought to do things conducive to happiness.
...I would call this conclusion a non sequitir. Essentially, (4) is saying that "you value happiness; therefore you ought to do things conducive to happiness." As discussed when we defined "ought," we can potentially interpret this statement as saying that "It is objectively moral to do what is conducive to happiness. But this conflicts with the requirement that we establish an objective morality, as the evaluation process given in (1) is surely subjective. Even when different people are presented with identical scenarios, it is not uncommon for them to evaluate courses of action differently and come to different conclusions as to what the best action is. Controversy over, say, the Trolley Problem is a wonderful illustration of this.
Furthermore, using the "objective morality" definition of "ought," this argument is saying that doing things conducive to happiness is objectively moral before concluding that objective morality exists in (7). It thus begs the question to be using the word "ought" before we reach the conclusion.
On the other hand, if we stick to the "obligation" definition of "ought," I suppose it would follow that you're obligated to do things that make you happy given that we're assuming that "you" is indeed a free agent? But even ignoring objections raised in (3) that challenge the free agent assumption, this seems to be playing with definitions. Yes, I'm obligated to what makes me happy in the sense that I have no choice but to perform the action that I have evaluated to be the best, but not in the sense that I have a responsibility to do so.
- Define morality as the set of habits/behaviors/attitudes conducive to socialization.
Within the context of this argument, this is a definition and not open to objection. However, if this argument were applied outside, it would certainly run into objections here. People who affirm the existence of objective morality would probably not define it like this. However, this is the definition we'll work with as we continue.
- Since humans are essentially socially-oriented creatures, it is overwhelmingly likely that humans who develop moral behavior will be happier than those who do not, ceteris parabis.
The problem here is that if there exists even one antisocial human, then for them, social (moral) behavior would not lead to their happiness. If it doesn't lead to their own happiness, then from (4) we conclude that it must be either objectively immoral or non-obligatory ("non-obligatory" in the sense that social behavior won't be the action they must choose to remain a rational agent, as they'll evaluate social behavior to be suboptimal), depending on the definition of "ought" we use. Whichever definition we choose, for antisocial humans, (4) is forced to conflict with (7).
- Thus you ought to be moral.
The conclusion again begs the question given an "objective morality" definition of "ought," since (7) depends on (4), yet (4) assumes that (7) is true.
So in conclusion, a list of potential objections:
- The definition of "happiness" is ambiguous.
- It is a controversial assumption that "you" are a rational agent.
- Rational agents undergo subjective evaluation processes.
- A "moral" definition of "ought" forces (4) to assume the conclusion.
- An "obligation" definition of "ought" seems to force (4) to play with the definition of "obligation."
- This argument adopts a controversial definition of "morality."
- Not all humans are socially oriented, and for those humans, (4) conflicts with (7).
- (7) depends on (4), which begs the question under a "moral" definition of "ought."
