On any given day, one in 30,000 Americans will conceive a child. So, roughly, there is a one in 60,000 chance that someone you (I'll just assume you're in the US for convenience) are interacting with will be conceiving a child later that day. Any interaction you have with a person who will be conceiving a child later that day is likely to affect the exact time of conception, and it seems very likely that varying the time of conception will vary the genetic identity of the child conceived. However, there might be some "resetting" mechanisms throughout the day, mediated by the way our days are governed by times of meetings and so on, and so not every interaction will change the time of conception. So let's say that one in four interactions with someone who will be conceiving a child later that day will vary who will be conceived (or whether anyone will be). That means that one in 240,000 interactions we have with people affects who will be conceived on that day.
Once one has affected who will be conceived that day, as long as the human race survives long enough, eventually just about everyone's genetic identity will be affected by one's actions. For, obviously, that conceived individual's own children's genetic identity will be affected. But that individual will interact with others, affecting the romantic decisions or at least times of conception of others, for instance. It seems quite safe to suppose that that individual's interactions over a lifetime will affect the genetic identity of ten individuals. Given an interconnected world like we have, it seems reasonable to suppose that in 20 generations, almost everyone's genetic identity will be affected (maybe there will be some isolated communities that won't be affected--but I think this is unlikely).
Counting a generation as 30 years, a blog that has 240,000 hits per year, running over a single year, will affect the genetic identity of almost everyone in 600 years. And this, in turn, will affect all vastly morally significant things where individuals matter: the starting of wars, the inventing of medical treatments, etc.
It is very likely, then, that the long-term effects of such a blog in terms of reshaping the world population vastly exceed whatever good and ill the blog does to the readers in the way proper to blogs. After all, one more or one less warmongering dictator and we have millions people killed or not killed. So the kinds of considerations one brings to bear on the question whether to have a blog--how will it affect my readers, etc.--are swamped by the real variation in consequences. (Assuming Judgment Day is still hundreds of years away.)
Not to be paralyzed in our actions, we need to bracket such great unknowns, even though we know they are there and that they matter more than the knowns on the basis of which we make our decisions!