I could never get my head around the Refusal ending. If you have the ability to defeat the Reapers, why not do it? Do you not think that the people in the next cycle would horde the technology like the Asari did?
Shepard pointing a gun at the Destroy tube and shooting is him shooting EDI and the entire Geth. As well as directly deciding to cause the damage to organics that the effects of even High Destroy will bring.
There's easy RP paths to make that acceptable but not necessarily. There can be Sheps that you can believe are not willing to be so direct in their murder of, at minimum, millions of possibly sapient beings.
Personally I see Refuse as a barely-covert patched in Fail ending, but its not a fail because Shepard lacks the guts to take action (exactly), but because Shepard lacks the will to become so much like the Reapers that his influence and actions affect the galaxy to such a disturbing degree.
Here's a gun. Shoot it and it'll kill all Germans and Japanese and Italians but it'll end the World War. Go ahead. Shoot it. Okay, its not as clear as the Reaper threat, but we can or do gain enough seemingly likely legit info that indicates that destroying the Reapers, while its our 'job', is not necessarily the way to go. So we're bound by choices and all of them are too much to stomach - even a higher EMS Destroy. So we don't be bound by them, and refuse. So the next cycle does better, Shepard is not so much of a 'destroyer' that he kills so many of his supposed allies himself, yet his inaction doomed the last cycle and gave him a lesser legendary status than otherwise.
Refuse = I'm a man/woman of action but damn, this is too much. I cannot and will not be responsible for existence for such a degree. I'm human, not a god.
Of course it makes less sense to pick it in High EMS but especially in Low or Super Low EMS... its potentially compelling.