Why are some denominations so against the idea of personal revelation as a source of Truth?

In the spirit of https://christianity.stackexchange.com/questions/12584/on-what-basis-do-some-denominations-prohibit-christians-from-drinking-alcohol and https://christianity.stackexchange.com/questions/10051/why-do-young-earth-creationists-make-such-a-big-deal-about-the-yec-view First, what this question isn't: - It is not asking whether the gifts discussed are still valid today. (That's been asked already). - It is not asking if the Ongoing Revelation as believed by some denominations is ***valid*** or ***true***. - It's not about asking for a Scriptural reason. As noted in the question linked to in the first bullet point, Scripture can be interpreted either way on this. Put other way, ***this is not a "Truth" question***. It's a question of the cultural and doctrinal understandings that leads to adherence to a particular view. In other words, what are some of the reasons some Christians are so wary of a view that other Christians are so willing to embrace? --- Many of the Pentecostal denominations believe that things like speaking in tongues, prophecy, and ongoing revelation are still happening today as ways for God to provide us with Truth. Likewise, the LDS Church believes in continuing revelation to the Church through the Prophets , as do others . Some of the more conservative/Fundamentalist denominations believe that extra-Biblical revelation stopped with the closure of Canon , and tend to view modern day practice of these types of personal revelation as false, and even dangerous. Most people can understand the Scriptural arguments, which would lead to believing that such a view is either true or false, but why ***dangerous***?