A long time ago, I submitted a story to a writing challenge where a character in impossible circumstances (because aren't they all?) cheats on her husband.  A fellow writer / critiquer said they enjoyed the story, but had trouble with that aspect.  I said that I'd had trouble writing it, and the response was ... "So why did you include it?"

Not a bad question.

This aspect in film / fiction has always been a pet peeve of mine; I find it difficult to sympathize with characters in that position.  And that is why I did it.  I challenged myself to take on a perspective I didn't agree with and do it sympathetically.

As a writer, I think this is an important exercise; as a speculative fiction writer, doubly so.  If you write antagonists, chances are they espouse positions that don't align with those of your main characters (and we'll assume that usually, main characters have morals and ideals similar to those of the writer).  Can you make the antagonist convincing without at least trying on his shoes?  Can you write a nonhuman character if you can't write a perspective that isn't your own?

And maybe the answer for some writers is they don't, whether due to interest or because they are trying to convey a specific message.  For me, though, I like squishing around in heads that aren't my own, though I could always do a better job of it.  Maybe it's high time I visit a foreign (mental) land again.