Well, I think we’re going off on a bit of a tangent from the original question, but I’ll bite. The test in Matthew 7:16-20 is defined in scope by the preceding verse, Matthew 7:15, which demonstrates it is to be used to guard against false prophets. Now, we could surely apply the test in many areas of life in a beneficial way, but that is the specific Biblical context, and that’s the only context in which it is spiritually authoritative.
Granted, some churches would qualify as false prophets, and so that test can be appropriate. However the specific question at issue is how to, or who can, interpret Scripture. Unless one argues that merely questioning the Catholic church’s claims on the matter is equivalent to false prophecy, then I don’t see how the application of that law is warranted in an authoritative sense.
As for the question of who is going to heaven or hell based on what standard, well that’s a matter for a whole other thread (or a few thousand threads probably). Personally, I don’t like to take a position on what the fate of any individual person will be, since I am not the appointed judge of their fate, so I simply don’t know. So, I think it’s a bit fruitless to speculate on the fate of Mother Theresa, a criminal, or yourself. I will say that I think any “fundie” that has told you with certainty that they know where you’ll end up should probably spend more time worrying about where they will end up instead!
Indeed, what makes modern liberalism and islamofacism so dangerous is that they seek to transform their false religion into a top-down command and control political system.
And, btw, I agree with you on the Taliban Christians who appoint themselves as God's spokepersons to determine who goes to heaven or hell.
I also don't see a wall of separation between political truths, religious truths or scientific truths.