I don't think there is a moral problem, unless the blog says that the its content is made of your daily thoughts or something like that.
Ultimately, is not the day you wrote it, but the day you thought it that could matter. If you write your idea on a notebook to make it a post later won't make any difference to your reader and will only harm your writing process.
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You have a point. "Blog" is short for "weblog" or "web log" -- and too many of us were brought up on Captain James T. Kirk faithfully recording the unfolding events on Stardate whatever-whatever. Diaries / journals on paper carry the same weight of compulsion and guilt -- historically a daily account, so that's what some corner of our mind seems to expect. Easier sometimes to think of a blog as a publication or news cast or editorial column or such, rather than a "log" per se: maybe it is published hourly, daily, weekly, or somewhere in between... the frequency doesn't seem to matter as much as a certain consistency, if you look across the range of posting schedules in the so-called A -List. Hard to get out from under that niggling little "shoulda posted today" guilt, though, isn't it?
I think that is truly what blogs are becoming. Actually, one of the reasons I began blogging was that I actually wanted to produce a daily column. I was successful for almost a year--then I realized that I was doing a lot of work. Especially, when I changed chaplainandrews.com over from a static site to a blog.
And yes, I have a terrible time shaking the "I hafta blog today" guilties.
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