I understand your desire...
The problem just is that just like no two persons have the same idiolect, no two persons have the same perception of the "language as such". We learn it by example, and mostly before we've developed any kind of stringent deductive reasoning, in early childhood. It's hard to get a firm hold on emergent entities - and that's putting it mildly.
I don't agree with willy-nilly disregard for one's own experience of language, but I also don't agree with setting down arbitrary rules for language. You are entitled to your view of "since", but what if I ask you how you know it's wrong to use it for evidential causality marking?
What if someone says that "due to" can't be used except for describing money owed (an old teacher hobby horse), and that it can't be used to mean "caused by". How can they know? And how can we know if they're wrong?
What if someone says that "it follows" can only be used to mean that something moves along the path traveled earlier by something else, that "follow" can't have metaphorical extensions?
We get to a slippery slope when we start saying which change already happened must be rolled back.
That's what I am saying.
