A sentence with italics or any other emphasis should read exactly the same without that emphasis. Where the same isn't true of capitalisation.
Not true. In conventional English, it is typical (if not expected) to add verbal emphasis to italicized words while reading aloud.
But it doesn't, that's the thing! The word you italicize can alter the meaning of a sentence. For instance:
> "I didn't steal Sally's necklace!"
> "I didn't steal Sally's necklace!"
> "I didn't steal Sally's necklace!"
I didn’t say I took the money.
I didn’t say I took the money.
I didn’t say I took the money.
I didn’t say I took the money.
I didn’t say I took the money.
I didn’t say I took the money.
• The first version implies that I acquired Sally's necklace via other means.
• The second version implies that I stole someone else's necklace.
• The last version implies that I stole something else from Sally.