I don't think that the person mistakenly believes that the consequences will be sufficiently worse, but something more like that the rule of not murdering people is really really important, and the risk that you're making a mistake if you think you've got a good reason to violate it this time is too high. Probably that's a miscalculation, but not exactly the miscalculation you're pointing to. I'm also just generally suspicious of the value of excessively contrived and unrealistic examples.
I'll take two broader examples then- "Broad Trolley cases", cases where people can avert a harm only at the cost of triggering a lesser harm but do not directly cause it, and "Broad Fat Man Cases", which are the same except such a harm is directly caused.
As a general rule, although humans can be swayed to act in Broad Fat Man cases they cannot help but feel bad about it- much less so in Broad Trolley cases. Admittedly this is a case in which humans are inconsistent with themselves if I remember correctly as they can be made to cause suc...
My apologies if this doesn't deserve a Discussion post, but if this hasn't been addresed anywhere than it's clearly an important issue.
There have been many defences of consequentialism against deontology, including quite a few on this site. What I haven't seen, however, is any demonstration of how deontology is incompatible with the ideas in Elizier's Metaethics sequence- as far as I can tell, a deontologist could agree with just about everything in the Sequences.
Said deontologist would argue that, to the extent a human universial morality can exist through generalised moral instincts, said instincts tend to be deontological (as supported through scientific studies- a study of the trolley dilemna v.s the 'fat man' variant showed that people would divert the trolley but not push the fat man). This would be their argument against the consequentialist, who they could accuse of wanting a consequentialist system and ignoring the moral instincts at the basis of their own speculations.
I'm not completely sure about this, but figure it an important enough misunderstanding if I indeed misunderstood to deserve clearing up.