would as soon do X as do Y

[imchongjun]

Could you tell me if I understand correctly the sentence in bold in the following passage?

"Oh, that is an old door connected with another passage that leads by a dark and wearying staircase to the servants' corridor beneath! I am afraid you won't be able to open it, as it is rusty with age and disuse. The servants would as soon think of coming up here as they would of making an appointment with the Evil One; so it has not been opened for years." (The Haunted Chamber by "The Duchess")

I understand the sentence means "the servant would never dream of coming up here." My reasoning is as follows: the phrase "would as soon do X as Y" means "I would do X rather than Y," so the sentence means that the servants prefer coming up here to making an appointment with the devil. But "making an appointment with the devil" is a...how should I say...an extreme alternative. If the servants were forced to choose between "coming up here" and "making an appointment with the devil", they would choose "coming up here," but unless they are cornered into such an extreme situation, they would never think of "coming up here".
Am I correct? or mistaken? I appreciate your help very much.

 

[teechar]

I understand the sentence means "the servant would never dream of coming up here."

Right, but see below.

My reasoning is as follows: the phrase "would as soon do X as Y" means "I would do X rather than Y,"

No. You are confusing that with "would sooner do X than Y".

The servants would as soon think of coming up here as they would of making an appointment with the Evil One

The servants would consider coming up here as much as they would consider making an appointment with the devil.

 

[imchongjun]

Thank you, teechar, for your reply.
The Chambers Dictionary says

as soon ... as ... used to state that the first alternative is slightly preferable to the second • He'd just as soon die as apologize to her.

So I think there is not much difference between "would as soon...as" and "would sooner...than" though I suspect the former sounds more old-fashioned.
Anyway it is good to know my interpretation is not off the mark. Thanks a ton.

 

[5jj]

The servants would as soon think of coming up here as they would of making an appointment with the Evil One;

This does not mean that they would prefer coming up here to making an appointment with the Evil One.

 

[imchongjun]

Having reread the posts, I suddenly realized that teechar is right. Yes, I was dumb! Thank you!