The Fundamentals

There is much diversity of opinion when it comes to religion. Though many believe that the bible is inspired, inerrant, and the source of all doctrinal truth, there is still diversity of opinion. The problem is that we don't always agree on what it says about a certain topic. Does this lead to some sort of justification for religious pluralism or off the wall cultic beliefs? Absolutely not!
Ultimately there will be strange cults and major denominational divisions. Even among "bible believers." But this is not to say the fault lies in the bible. The fault lies with the interpreters of the bible. How can we then be consistent in defining how one is saved, what a Christian is i.e. how do we know what constitutes Christianity?
With scripture twisting rampant in our day what are we to do? Even "solid" denominations have their disagreements. And the protestant reformation (the split of the accepted Catholic church) was not due to some far out weird teachings, but a somewhat complex defining of justification.
Whatever the case is (cults or mainstream disagreement included) there are certain fundamentals that we can not compromise and still be doctrinally and consistently sound Christians.

Here are a few examples of fundamental beliefs that cannot be compromised.
The way of salvation is one such fundamental. Though we may disagree on eschatology (the study of the end times) we cannot disagree on justification by faith alone and still call one another orthodox. Also we cannot esoterically view the bible as inerrant and fallible and both be considered orthodox. This allows inconsistent open progressive revelation with various sources of authority for one and not the other. Contradiction is inevitable. The deity of Christ is another non-negotiable.
We must have some fundamental beliefs that are not such that they can be disagreed on. These fundamentals define us and all of orthodox Christianity.

Here is an example of a non-fundamental.
You may notice that I have links to some that are dispensational in their eschatology, and links to others that hold to a different eschatological opinion. Does this allow one to infer that there is a fatal inconsistency? No! Such disagreement does not compromise any fundamental to the faith. It does not require us to break of fellowship with one another. Even though the debate gets heated there is no warrant to separate foundationally. Both sides are still Christian even though they cannot agree as to the final stages of the end of things. There are numerous other such examples. In conclusion:
We do not disagree over the way of salvation. Ever! It is a fundamental requirement for legitimately being Christian.