Carolina Sartorio argues that ordinary morality is committed to a kind of status quo bias, or what she calls 'moral inertia' [pdf]. The basic idea is that we need stronger reasons to justify interfering in a process (e.g. deflecting a trolley) than to justify abstaining from such involvement. The intuitive force of this claim is illustrated in two cases:
(1) The 1/1 trolley: a trolley is going to kill X unless you switch it to the side track, where it would kill Y. All else is equal. Sartorio claims it is impermissible to pull the switch, though it would do no more harm than leaving things be.
(2) The 5/3/1 trolley: a trolley is going to kill 5 people, unless you switch it to one of two other tracks. Side track A would kill 3 people, whereas side track B would kill just 1. Sartiorio claims that it is impermissible to switch to track A, but permissible to either switch it to B or do nothing (even though this leads to more harm than switching to A).
I'd offer a different diagnosis of these cases. In case two, I think the agent has decisive reason to switch to track B. Doing nothing and letting five die is not as justified an option, though it might be excusable if the agent's psychology is such that they would be traumatized by the thought of having "killed" someone (as opposed to merely "letting" five die).
In case one, either option seems permissible to me. Sartorio points out that it would be odd for an agent to pull the switch, since there's no reason to -- we might suspect that they had some special grudge against the person on the side track -- but this at most counts towards evaluating the agent as perverse (or possibly blameworthy, if they acted from malicious motives); it doesn't show the act to be opposed by decisive reasons (or indeed any reasons at all).
To bring this out, suppose that the agent has an ingrained habit of pulling switches, such that it would require more effort on his part to "stand back" than to just let himself go and pull the switch. (I should mention that I wasn't the only person in our seminar to be thinking along these lines.) It seems to me absurd to think that he is morally required to hold himself back in this case -- what would it achieve? Someone's gonna die either way, and you've no reason to prefer it to be the first person. In this case, it seems to me that putting in the effort required to do nothing is what would be perverse.
Sartorio might accommodate this intuition (as she does in a similar case where the switch is triggered by merely breathing) by suggesting that we build the dispositions of the agent into the 'natural circumstances'. Moral inertia then supports the agent's "going with the flow" and triggering the switch. But if we go this far, where do we stop? Isn't the agent's deliberative disposition a part of nature too? So whatever the agent ends up doing, that's the 'natural' thing to happen, given that the agent himself is part of the natural process. But then the moral inertia thesis is trivialized.
A related puzzle: even if (for some mysterious reason) we should not view ourselves as part of the natural process in this way, does moral inertia also give bystanders a reason to try to tackle an interfering agent before they pull the switch? Or should we at least view other agents as part of the natural process, and so refrain from getting involved ourselves?