Actually if you think about it Satan's fall is intentional. If you believe that angels do not have free will, then God must of willed it for him to rebel. Thus making the existence of Satan within God's will. Sure you can pity him, but he was created (assuming you believe the aforementioned stuff) to entice humans to do evil. He is rightfully blamed for causing evil since that is his role. He is God's adversary, in the most literal sense. Satan means adversary.

This is all assuming that you are Christian or believe in some Christian doctrine. Also a Satanist are typically people who worships Satan, in whatever regard. Pitying him is different from worshiping him.