The usage of the modal verb "should" (Should it not fear the light?)

Factual Questions
1

This is an ESL question.

I have difficulty understanding the usage of should in the context immediately below, would you please explain it?

Character A: I do not understand how evil walks in the day, **should **it **not **fear the light?
Character B: Perhaps, the sun is neutral.
Character A: But the light is both a literal and figurative foe of evil!

I think this usage of should is similar to the usage of would in the sentences below:

It **would **be fun to have a beach party. (The person expects he/she and his/her friends will have fun when they have a beach party)
It’s no use talking to Henry – he **wouldn’t **understand. (The person does not expect Henry will understand.)

So, I think the character A expects that evil fears the light. But because of something that he sees or hears, he starts questioning his belief that evil fears the light.

Therefore, I think we could say that the use of would indicates expectation in some contexts, and, the modal verb should can be used, instead of would, when the writer or speak wants to indicate an expectation, in order to sound more formal.

Many thanks

2

No, “should” is not a more formal version of “would.” “Should” refers to a requirement. Character A does not only expect that evil fears the light. He also expects that evil is required to fear the light. He expects that evil must fear the light.

“Should” and “would” never quite mean the same thing. They can be very close, or they can be very different. I will use your examples:

“It should be fun to have a beach party.” The person expects that a beach party must be fun. This is very similar to “It would be a fun to have a beach party.”

“It’s no use talking to Henry – he shouldn’t understand.” The person expects that Henry is required to not understand. This is very different than “It’s no use talking to Henry – he wouldn’t understand.”

3

I have an different reading of the former with “should.” It seems to imply that it ought to be fun, but probably won’t be. This could be explicitly stated, but it could just be implied by the way it’s said.