Basis for religious tolerance...well, we might have to look at history. In the past, when one civilization takes over another, they annihilate the religious beliefs and force the others to convert. Eventually, someone from the religion being purge will go out and martyr himself. Then, everyone else rallies around the religion and fights back which creates domestic problems with the ruler and quashing rebellions is a waster of time and resources. When rulers began to assimilate the different religions into the ruling cultures, they saw less and less of the fanatics and martyrs. As a result, other rulers began to adopt religious and racial tolerance. In fact, it makes it easier to recruit them into your army. The mongols for example, did not just scare others into their military, they also assimilated the conquored into their culture. The defeated accepted the assimilation and joined ranks with the Mongols.
some religious individuals cannot practice it because they have been brainwashed into it. They only see their holy texts as the word of their personal "God". That is why politicans who are able to go outside of the "box" usually have less problems dealing with religion within their practiced regions.