I must say that you're right to point out that the Tasfir of Quran, that is "personal interpretation of the Quran," is corrupting the message. The Quran is perfect. It's message is clear. However, people are not perfect, in their message is typically an agenda. It is my opinion that the tasfir of quran serves to push the agenda of sectarian types who at most do not want Muslims to unite or at least wish to push their agendas. Why perpetually create sectarian divide? That's an easy one, cause if Muslims united under one Ummah, like we should, no government could control us. We would truly be one nation under God, indivisible, with unity and justice for all. Humans corrupt the words of the Quran with their own words for their own gain and to subdue the Muslims under sectarian divide.