非常有意思的问题。

先换个角度，变成肯定句

1）I would trust you as far as I could throw you.

as far as I could throw you. 你能把一个人扔多远，距离很短! 所以我相信你的距离和你扔人的距离等同，即：我信那么一点点。也就等于不相信。

2）I wouldn't trust you as far as I could throw you.

那这句话变成否定句了，不就等于完全相信了！！非也，这句话，还是表示不相信。比上面程度更强烈。表示严重不相信。

虽然你扔一个人扔不了很远，但你讨厌到要扔这个人了，也就是你的心理距离是能远就多远。而我不相信你达到“能远就多远”，那就等于非常不相信。