Art is the creation of beautiful things and to some people religious paintings are the only appealing things to some peoples eyes. So it should be considered as art. I am a strong religious person and and a big fan of art, and I believe that anything that is beautifully drawn or sung is art.
Religious paintings should be considered art, religion has been around for a while and people of any religion would draw pictures to worship their gods,goddesses, etc. And it should still be considered art because since the dawn of time paintings have been considered art. People would paint pictures of great hunts, or of nature so it could be remembered or studied. Religious paintings are the same. It shows of great events that have happened in that specific religion.