I'm sure busterdog doesn't want me speaking on his behalf but I think what he means (in which case I agree with him) is that what we believe determines how we behave, however not all our beliefs impact on our behaviour all the time. If someone suggested Jupiter as a good holiday destination your knowledge would probably determine your behaviour in that case, but as to whether you should go to the theatre or the cinema on satuirday night, probably not.
Even when factual knowledge (or presumed knowledge) affects behaviour, there is still the fact that not every behavioural choice is a moral choice.
In and of itself, the choice to go to the cinema rather than the theatre is not a moral choice. However, if we knew the nature of the entertainment provided at each, then, there might be a matter of morality involved.
As I understand it the creationists' argument against evolution (and by extension the age of the earth/universe, etc.) on moral grounds consists of two parts.
1. On the assumption that evolution "proves" the non-existence of God, those who were already immoral in thought and behaviour gladly accepted it as consistent with their existing inclinations, since is relieved them of any vestige of guilt or fear of judgement.
2. The assumed implications of evolution (esp. that we are "just animals") encourages immoral behaviour in those who accept the theory, as there is no justification for behaving otherwise.
So immoral behaviour is both a ground for accepting evolution in the first place and is further spurred by accepting evolution.
However, if evolution is simply the fact of nature that TEs presume it to be, then it is no more immoral to accept it than to accept gravity.
The question rises again when we look back to the geocentric/heliocentric controversy.
Here we can at least do away with the notion that either theory contested the existence of God.
So, was geocentricity in any way grounded in immoral inclinations? Did it lead to immoral behaviour?
If the answer to both is "no", in what sense was believing this error of fact a sin?
If the question of the age of the earth falls into the same category of knowledge as the position of the earth in the cosmos, what makes holding the erroneous view (whichever you think it is) a sin?