"Why do you care?"
There are places where a sick child is attended to, not by qualified medical help, but by community members standing around performing a ritual of laying of hands, or chanting, or praying in the name of deity X when medicine is in a cabinet just a few feet away.
There are people who are stuck with a bad lot in life and rather than work hard to fix it, they choose to kneel down and pray for intervention from some god. There are people who, in the face of hard science, still choose to believe the Bible as quite a literal, instead of allegorical, slice of history. I could go on here, but you get the point.
Individually, nothing I ever say or do will change those people's minds or beliefs. It won't happen. And I'm fine with that because all their Bible thumping won't do the same for me*.
So here's why I care. Because those people get elected to local offices that become state positions that become federal jobs as Senators and Representatives. These people are on school boards, city councils, and are my neighbors. They will teach my child, perhaps be my boss, and I may be theirs as well. No amount of effort short of living as a hermit will allow me a life not around people who have beliefs different from mine. Either I learn to deal with it or I become very miserable and cynical. Like I said before, I won't change, they won't change, nobody is going to change their long-held beliefs. So rather than fight what won't change, why not get a better understanding so that we can find more common ground to agree on than nits to pick. Perhaps they can see that 'heathens' such as myself can be just as virtuous and 'good' even though I don't parade around with a cross dangling from my neck and likewise, I can see that people I think are blinded by faith can have common sense and reason. We learn more when we can include more.
So that's why I care and enjoy discussing religion.
*I am a Christian (or optionally 'Christocentric') Deist -- I believe that our universe was created by a God who does not interfere, intervene, nor specifically cares how individuals lead their lives. Son of this god or not, the teaching of Jesus that became the basis for Christianity are a good basepoint from which to determine how you live your life. This is not to say all points of Christianity are good nor does it say that other religious beliefs don't have merit, it's just a starting point, and that this creator gave each person the gifts of reason and intelligence enough to form their own beliefs.