I think part of the concern is that when you try to make ethics explicit you are very likely to miss something, or a lot of things, in the 'rules' you explicitly lay down. Some people will take the rules as gospel, and then there will also be a risk of Goodharting.

In most games there are soft rules beyond the explicit rules that include features that are not strictly part of the game and are very hard to define, such as good sportsmanship, but really are a core part of the game and why it is appreciated. Many viewers don't enjoy when a player does something that is technically allowed but is just taking advantage of a loophole in the explicit rules and not in the spirit of the game, or misses the point of the game (an example from non-human game players is that AI speedboat that stopped doing the actual race and starts driving round in circles to maximise the reward. We like it as an example of reinforcement learning gone wrong, but it's not what we actually want to watch in a race). People who only stick to the exactly explicit laws tend to be missing something/be social pariahs who take advantage of the fact that not all rules are or can be written down.

do you think there are principled reasons to think that the more “explicit” ethics of effective altruists is actually a bad thing? Or should we take this causal explanation to be, in effect, a debunking explanation of why many people are unreasonably opposed to EA (and to goal-directed ethics more generally)?

We discuss this in our preprint. 

We find that people evaluate those who deliberate about their donations less positively (e.g. less moral, less desirable as social partners) than those who make their donations based on an empathic response. But a possible explanation of this response is that people take these different approaches to be signals about the character of the other person:

Namely, donating empathically may signal that one has good moral character and is a valuable social partner, because reacting empathically communicates an inclination to help those in need and a reliable motivation to behave prosocially. Supporting this, research has found that people infer that those who rely on emotion are more likely to cooperate and are more likely to feel emotions like empathy (Levine et al., 2018). Additionally, research has shown that donors who experience greater empathy are perceived to have a better moral character, and that this effect is reduced when the emotion felt does not lead to prosocial behavior (Barasch et al., 2014).

In contrast, deliberating about cost-effectiveness may be perceived as a weaker indicator of prosociality, as it suggests that donors are motivated more by pragmatic considerations than by concern for recipients’ feelings. As a result, deliberative donors might withhold assistance in situations where the aid is not deemed cost-effective enough, despite a compelling emotional appeal from the individual in need. This could lead observers to infer that deliberative donors are more cold, calculating, and pragmatic, with weaker commitment to interpersonal relationships. Similarly, research on judgments of individuals who make consequentialist decisions—such as helping a greater number of strangers rather than a single family member—indicates that they are less favored as partners in close relationships (e.g., friend, spouse) and are perceived as less loyal (Everett et al., 2018). Moreover, research has found that helping strangers instead of close others (e.g., friends, family) is deemed morally unacceptable and may have negative relational consequences (Law et al., 2022; McManus et al., 2020).

I think this suggests that individuals may have good reasons for their negative evaluations, as people who deliberate about the cost-effectiveness of their aid may be less likely to provide aid in the kinds of typical cases which people normally care about, than someone who aids due to an empathic response (e.g. they may be less likely to help the person themselves or someone close to them if they are in need). But, of course, this doesn't show that deliberators are worse, all things considered, so I think this remains quite viable as a debunking explanation.