Discussion: Should authors discuss real world issues in books?

First, forgive me for being a little late posting my weekly discussion. This previous weekend I was celebrating my birthday and I honestly forgot to type a discussion up until right now. 
Now, onto the discussion.
It’s no secret that I seriously enjoyed Mark Charan Newton’s books (my reviews of them can be found in my Great Index of Reviews). One of the big reasons I enjoyed them was because Newton applied a lot of real world problems, like sexuality, environmental and class issues, to his plots in a big way. I thought this was bold and I admired him for using real world themes in his books as it may help people think about these issues in a new way. 
However, not everyone is a fan of authors applying real world themes to their books like Newton and others have. For example, some readers may feel that this is evangelizing beliefs or perspectives and not appreciate that interspersed into their books. Yet others may think that this is something authors can’t ever quite avoid adding to their work.
Thus, my discussion for the week: 
Should authors discuss real world issues in their books? Why or why not?