1) That's a personal decision. In my opinion it is not morally wrong at all. I enjoy it.

2) I don't know about porn vs erotica. It all comes in various flavors so to speak. I've always gone by the rule that as long as all parties involved are of age and consenting, it's fair game. I can't judge you on your tastes as yours are very mild compared to mine.

3) The easiest option is probably to stop discussing it with them. Beyond that you have every right to be unapologetic. You say how you feel, they say how they feel and you agree to disagree. There is nothing to defend.

I am not Christian. I'm a total free spirit and I'm pro just about everything to do with sex. So take my advice for what it's worth to you.