So honestly, I'm not even really sure why this question seems like such a pertinent one, or why authorial intent has become such a worry for people at this stage in the game. I think I got those worries Freshman year starting out the English major, but at this point I think I've either internalized enough of the rhetoric, or (hopefully) come to understand something about literature that pushes me away from any worries about over-close-reading.
So here's my pitch, as it applies to both Huck Finn and any other piece of literature we might worry about textual ownership for or close reading.
1. What's the purpose of analyzing a text at all, close reading or not?
I'd imagine that we aren't going to say that it's to find out what the author wanted to say. If we wanted to find out an author's thoughts, we could ask, and if an author wanted to express thoughts on an issue clearly, (s)he'd write a paper on the topic, not a work of fiction. At the very least, the author's intent doesn't seem to be what we're getting at when we read a text.
Perhaps then, we ought to think that there's something more, something deeper. What is it? I'd propose that analyzing a text can do (at least) two things for us.
2a. Understanding a context, functioning as a social mirror. Works of fiction are products of their socio-political climate. They reflect things the author is exposed to, sometimes things they're not even aware of. They can reflect social oppression or social progress. They can show us what an author experienced, or what an author thinks (s)he experiences in his/her life.
By reading Huck Finn, for example, we get a picture of a time and place as interpreted by Twain. Even if Twain's read on the time/place is factually inaccurate, either by his deliberate manipulation or by subconscious social influence, we still get an understanding of how people like Twain understand their social climate, or the social climate of the time they're writing about.
2b. Hearing critique, deliberate or accidental. Authors sometimes write about what they see. Sometimes they don't like what they see, or aspects of it. Sometimes they do. Nonetheless they provide us with arguments via their observations and biases that we can choose to agree or disagree with. We can flesh out whether their observations are accurate or not, and we can decide whether their arguments are coherent and well thought out.
3. So, I think we should conclude that literature belongs to the interpreter.
It belongs to whomever is interested in viewing and considering it. It belongs to whomever is interested in pitching an argument about it's meaning in the context of the society the work exists in.
Huck Finn is a window into 1884, 1835-1845, and into today. It gives us a read on our history, on race relations, on how we ought to think of them, how we might work to change or improve them, among other things.