But if I say "I believe there isn't a Tooth Fairy" and you say "I do not believe there is a Tooth Fairy" aren't we both going to hurt Her feelings (if She exists)?
The statements are not equivalent. Per my original post, the first statement is an affirmation of the Tooth Fairy's absence. The second statement is one of mere absence of belief, which is a separate logical construct with a different target. If I say "I believe 1 BTC will never be valued at USD $1000," the message conveyed carries different referential weight than the statement "I do not believe 1 BTC will be valued at USD $1000." The latter statement isn't affirming anything, instead conveying a message of mere present lack of belief; no valuation judgement is made. As for any feelings or lack thereof on the part of any supposed deity, I really couldn't offer an opinion either way.
Sorry, I think that your thinking and language is theistically-slanted
It's really not the topic of discussion here, but perhaps it will help to understand that I am not a religious man.
does not have to mean that I am opposed to the very idea of X
Especially in terms of common literary devices and societal norms, that is absolutely what it means. There is a reason the terms "agnostic" and "atheist" are separate words, and they are not to be taken as synonyms in all but the most inexact of contexts. Therefore, to attempt to subvert this reality for the sake of imposition of your particular personal interpretation of these words in general conversation is to hazard being misunderstood.