Lots of things are "just theories" but honestly that word does not mean what most people seem to think it means. As far as I know music theory doesn't talk about how to write music, it just explains the relationships between tones. There is also an "excepted" way of utilizing this information which has more to do with culture and personal taste.
The word theory is often used to try and say things don't count or are up for discussion because, hey "it's just a theory". But honestly the word theory is much more substantial than that. For instance by the time something becomes a theory in science than it is usually very well developed and has a lot to back it up. It isn't something that comes about before there is very substantial evidence to back it up.
The word theory is one that sort of has a common usage meaning and very different formal meaning.
Scientific theories (including music theory) are of the latter usage of the word. For instance the "Theory of Evolution" (i don't want to get into a discussion about this it's just a god example) is actually backed by mountains of data and evidence. It is not a theory in the sense that it is just an idea some people have about how things might have happened, it is well established and supported by, like I said, mountains of observational data and observable evidence in the form of fossils and other biological records.
In the same way music theory is not "just a theory". It is measurable and verifiable. It is not up to interpretation whether or not certain tones have certain relationships. It is just a fact of the system.
I don't know if that has anything to do with whats being discussed but it seemed relevant.
The word theory is not a license to think whatever you want and disregard logic and fact. And btw the way:
[qoute]
And that leaves plenty of room to interpret what you believe to be fact. [/quote]
fact is not whatever you want to interpret it as, it is fact. Two people cannot interpret data two different ways and it be fact to both of them. Either one of them is wrong or they both are. Logic is a language and a way of thinking that allows fact to exist to us.
But 440 hertz is 440 hertz no matter what.