Legislation should not be influenced by religion in today's modern world due to the fact that if laws and legislations were to use religion as a basis for its system, then who says that an individual claiming that in his religion they need to sacrifice 1000 people every month as a ritual for a outer god, could not use his argument about his right to use his religion to enforce genocide.
Legislation made with religion can lead to extreme laws dooming a society to an extreme in either side of the political spectrum