Example from my own writing:
I cupped my nose—when I should have covered my ears. To block the wicked mocking of my classmates.
I was told by another writer that I should avoid this kind of writing. Is he right? Or consonance is actually desired in fiction?
One of the worst things that happens in advice given to writers is that individual criticisms get inflated, either by the speaker or the hearer, into iron-clad universal rules. Thus, a perfectly reasonable "show this, rather than telling it" becomes a universal "show don't tell"; "remove this adverb" becomes "remove all adverbs".
The use of consonance may be wrong in this particular case (the sentence does not really pay off the rhythmic pattern established at the beginning). But that should not be inflated into a universal prohibition on consonance. There are no bad techniques, just techniques used appropriately or inappropriately and techniques used well or badly.
There is not a 'rule' about it being right or wrong, any more than there is one about alliteration. Judge what effect it has in a particular situation and then decide whether you want that effect or not.
I agree with Mark. I also don't care for your example. I don't have the full context, but it seems to me "wicked" is too strong a modifier for "mocking", which I tend to think of as harmless ribbing. But I grew up in an unforgiving neighborhood, so perhaps I am more callous than most.
If consonance in general appeals to you, I'd suggest it could be a character trait for one of your actors; sometimes funny, sometimes awkward: That's who she is, it could give her a distinct "voice". You can point it out by sometimes having other characters make fun of her for her more strained efforts at consonance.
I'm fond of consonance I find in prose when it reads fluidly. I don't understand why things that are considered useful tools in poetry should be avoided in prose.
And no one has mentioned it so far, but I like the consonance in your first sentence--cupped & covered--the similarity of the sounds goes nicely with the parallel structure of the thought.
