AntiTheist,
You’re using the extraordinary character of a claim as rational support for the strength of doubting it, thus justifying your doubt’s force. Think legally: “beyond
reasonable doubt.” If the claim were instead, say, [Barack Obama is President of the USA.], then certainly you would demand anyone who skeptically wavers about it, or suspends belief, to justify his lack of acceptance. You would rightfully call the guy irrational for
not believing. I think that’s Leela’s point: whenever a person makes any choice, whether it be to affirm, deny, or even just suspend belief, he is positively choosing a course of action, and so he presumably would require justification just to act at all. The mere presentation of a choice often unsettles a man and effectively leaves no possible “default” position of neutrality, i.e., forces him to actively choose a course, and would a rational man not still require rational support even in just his decision to refrain from acceptance?
Doubt is the active questioning of a claim’s truth, and it only typically entails wariness to accept that claim, i.e., to believe it. (Since “acceptance” just means affirmation
as true, a person’s positive mental entertainment of any assertion as not-true – a.k.a. false – naturally tends to weaken his acceptance of it, though not necessarily. I would actually wager that those who have most strongly doubted God’s existence were saints with concurrent faith.)
‘Doubt’ according to the Online Etymology Dictionary:
early 13c., from
O.Fr. douter, from L. dubitare “hesitate, waver in opinion” (related to dubius “uncertain”),
originally “to have to choose between two things.” The sense of “fear” developed in
O.Fr. and was passed on to English. The -b- was restored 14c. by scribes in imitation of L. Replaced O.E. tweogan (noun twynung), from tweon “two,” on notion of “of two minds” or the choice of two implied in Latin dubitare (cf. Ger. Zweifel “doubt,” from zwei “two”).
Any claim can and arguably should be doubted, at least minimally. To doubt an assertion x is just to consider its opposite’s truth, to entertain the possibility of not-x. The power of doubt, lying in its doxastic force and ability to move minds, will of course vary. For instance, I can doubt that I have hands, but I won’t then be disinclined to believe that I do, since I can clearly see that the proposition * is ridiculous, especially when weighed against * (namely due to the clear sight of the things typing in front of me). On the reverse extreme, I might doubt that I am the greatest basketball player in the world, which would instantly force me to reject such a claim. Every meaningful proposition will be either true or false; no middle ground exists between them. Whenever a new claim is proposed for belief, one wisely pits its warrants to truth against its opposing reasons for non-truth, and then he chooses to affirm or not. Everyone’s got a different threshold for acceptance, which is at the true heart of dispute between theism/agnosticism. When its doubt is extremely strong, the person will accept his self-proposed opposite claim, and that belief will logically cause him to outright reject the first proposition.
OK, so my point is: the justification of doubt itself is largely just practical; it serves as a sort of screening test for veracity and allows one to judge an appropriate level of confidence for a belief. However, the
power* of doubt must be rationally based, since it lies in the justification and support for a positively opposite assertion. Doubting God’s existence should only have force if there exist positive reasons in favor of affirming God’s non-existence.
Take your example, [a flying dog just taught you how to make gold out of lead.], and it’s obvious that the rational justification for the opposite claim far outweighs the reasons in its support. Dogs can’t fly, for one. Thus as soon as one doubts it, the warranted power behind the doubt should force one to reject the claim, let alone simply to not affirm it.
Now take an “agnostic claim”: [My grandmother’s favorite color is pink.], for instance. I analyze its rational merit and find virtually nothing in its favor. Now I doubt it, but the doubt has no power, since I know of nothing in support of her favorite color not being pink. Therefore, nothing tips the balance in favor of belief, so I currently lack any truth-relevant motivation for affirming the claim (though one might still succeed at a pragmatic sort of argument, say, a “Grandmother’s Wager”). Assuming no pragmatic justification, belief in the proposition isn’t rational, meaning that a rational man would suspend belief regarding it, i.e., affirming neither it nor its opposite.
So you’re right that a belief ought to be justified rationally, whether strong doubt is warranted or not. However, for a person to rationally let his doubt of a claim have any force, that doubt must itself carry rational support and be thus justified. In the end, if the rational support in favor of opposing propositions is equal, or even only barely in favor of affirmation (not enough to satisfy a warranted threshold), no one is rationally justified in his belief.
Agnostics believe that the God-question is like the grandmother-question. Positive atheists, which you seem to be, would assure everyone that the question is more like the flying dog-question (or perhaps like asking, oh say, whether there exists a magical unicorn on the far side of the moon). The subject of an agnosticism debate would revolve around a proper threshold for belief in such a being as God; the subject of an atheism debate would be much more theoretical and fact-oriented.*
is that atheism is a belief, although she may on the other hand simply be arguing according to a different definition of atheism 
