No reason justifies disbelief.

[BrianSoddingBoru4]

I thought I had, but I'll have another go.

Reasoned disbelief is the rejection of a proposition when there is neither convincing evidence nor compelling arguments to support the proposition.  Let's do Bigfoot as an example.  I disbelieve in Bigfoot because the evidence for Bigfoot simply isn't there - no bodies, no bones, no adolescents, no scat, no hair, no nothing.  Believers use all manner of specious arguments to explain away this (for them) disturbing lack of evidence: Bigfeet are too smart to get caught; Bigfeet are hyperdimensional beings; Bigfeet are aliens; and so on.  Given the non-existence of evidence and the non-compelling nature of the explanations, I make the reasoned choice to disbelieve that Bigfeet exist.

To be fair, there is also 'unreasoned disbelief'.  Things like, 'I don't believe in Bigfeet because I'VE never seen one' or 'My spirit animal told be not to believe in Bigfeet.' 

Hope this helps.

Boru

Why do you think reasoned disbelief for Bigfoot is the same as for the creator?

When it comes to the creator there is no reasoned disbelief.

It is the same for any proposition.

Then you'll need to supply either convincing evidence or compelling arguments (or both)  for a creator.

Boru