As Whitemane points out, the definition of scientific theory is not the same as the colloquial definition of theory as 'guess'. A scientific theory, such as evolution is defined (by Wikipedia in this case) as:
A well-substantiated explanation of some aspect of the natural world, based on a body of facts that have been repeatedly confirmed through observation and experiment...Scientific theories are the most reliable, rigorous, and comprehensive form of scientific knowledge.
I feel I have to also mention, Twyrch, that we don't even agree on the one point of agreement you speak of! Sorry!
I don't believe in any sort of 'intelligent design'. I think the facts as understood by science do not support that hypothesis, although I admit that we do not yet know everything about how the universe or life began. Still, I know that scientists are working on it and until then I find 'I don't know' far more satisfying than saying it must have been a supernatural designer.
But as long as people's personal opinions about the origin of life don't get muddled up with science and affect the education of impressionable young minds, I'm happy to agree to disagree!