Well, in Thay very least tieflings are not social outcastes usual cases (if not count background quirks like Ghaazala). In practice some tieflings are even red wizards (although PrC in DMG and faerun books say 'humans' but it should also count tieflings just lore wise).<br/><br/>Also Mulhorand the aasimar or tieflings are not outcastes but rather revered (tieflings more feared than aasimars but respected still). It's just rest of western faerun having problem with them :P.