Why are you angry? I didn't mean to make you angry??

I agree there are loads of books used to further political aims etc. Look at uncle tom's cabin, a book that had a really important message and sold really well in its time but is not remembered today at all because of it's boring moralism. Those books date horribly because they are just propaganda.

To kill a mockingbird has actually gone into a bit of controversy recently anyway with people saying it is a "white savior" book and I agree with that: because it is a political novel, a political novel pandering to whites, it had to ignore other perspectives and ends up with that trope which makes it bad art even if the political value is there. While there are certainly other merits to the book the fact that it is a "white savoir" novel is because it is a political novel aimed at whites.

Go set a watchman is by the same authour and while of questionable quality it gets rid of it's white savoir by making Atticus Finch deliver a racist speech. Now, because of the constraints of politics in To kill a mockingbird Harper Lee couldn't make Finch flawed in any way, she couldn't make his character have depth being a lawyer who did not care about the case because that would alienate the audience who wanted a simple moral message. See how politics restrain a work?

I also don't like the view that a novel should be about something. It is a remnant of the christian "story for social good". Not every work has a message or political aim. There's this play by Wole Soyinka called death and the king's horsemen in the introduction he says:

He resists the suggestion that Horseman is an essentially political play. In an introduction he wrote when it was first published, Soyinka issued a stern warning not to interpret it as a "clash of cultures" piece: "I find it necessary to caution the would-be producer of this play against a sadly familiar reductionist tendency." He still stands by this. "At the time," he says, "the tendency - in the theatre, the cinema and the novel - was to present everything that dealt with things outside western culture as being understandable only as a 'clash of cultures'. This covered everything, and it encouraged analytical laziness."

See how looking for a political message in a work isn't always the right way of looking at things? Not all stories are political, in perceiving the play as a simple "clash of cultures" tale we are ignorant to it's focus on human behavior and drama.