A dildo also isn’t able to consent. A carrot isn’t able to consent and is more alive than the roadkill (since it can still reproduce). Ability to consent is something we require from conscious beings, but we generally don’t require it from objects, and corpses blur the line.

I definitely get the “ick” feeling from necrophilia, so my knee-jerk reaction is to consider it immoral, but it isn’t actually that easy to come up with a consistent justification for that condemnation.