Every one accepts something as true unless they have gone crazy.
But it's possible to accept as true the position that ultimate truth is inaccessable to the human mind (as we can only experience the universe through our imperfect senses). Thus, it can be stated that nothing we can know is strictly "true".
But then, only a crazy or ignorant person sets up "truth" as a bivalent condition. The reality is, truth is a spectrum - some things are more or less true than others. Science is a process (for instance) where scientific models, over time, approach truthfulness.
I take the Bible to be true and where people have taken it upon themselves to add to it, I feel free to throw that out, especially if doctrinal issues are based on those alterations.
How do you tell the difference between something that was added and something that was "always there", especially in a work that has come down to you, translated through several intermediate languages? And how do you know that it's not the case that ALL biblical content was "added"; i.e. made up by people to support doctrine?
If you hold nothing but your own opinion to be true, you live as a solipsist. I hold that the Bible is true and my opinion is true only when it correctly follows the Bible.
Doesn't that make you a solipsist? If your assertation is that only the bible is true, but it's just your opinion that the bible is true (which must be the case, or everyone would agree with you), then haven't you, by extention, said "only my opinion is true"?
The truth of the Bible doesn't rest upon anyone's understanding of it.
If this were true nobody would have to interpret the bible. There would only be one church instead of thousands. Everyone would agree. That everyone
doesn't agree suggests that there is no inherent truth to the bible - it's all in interpretation. As Mr. P said, even literalism is a kind of interpretation - due, in part, to the mutability of language.