I'm thinking of sending my husband up into the pitch-black attic because he is afraid of the dark.
If you know that he's afraid of the dark, what is your reason for sending him up there?
My intention is that he would realize how hard it is to be alone in the dark.
He's already aware of how hard it is, since he is living with this fear of the dark. Making him go up into the attic does nothing but terrorize him. You should be trying to help him learn to face the dark, instead of just throwing him into scary situations like this.
I am his wife and I know what I have to do.
If you care for your husband, then you should be patient with him and help him overcome this phobia that he has. I'm sure you wouldn't want to be treated this way if you were afraid of something, so just show the same concern for your husband.