For me, spreading ignorance (or bad information due to ignorance) is an issue.
If you are gonna talk about subject X, make sure you know subject X, well enough to talk about it. At least, make sure that you are not making gross errors about subject X. Is it really too much to ask?
It bothers me on both the practical level and as a matter of principle.
I’ve been working as a professional programmer for years, and I’ve encountered many without basic scientific background. And that’s FINE! Not everyone needs it, or wants it. But then these people read a blog post, and it sounds right, so they believe it. After all, they lack the knowledge to figure out which parts are true and which are don’t. That’s why they are reading the blog!
And they learn stuff that is WRONG. And then they are going to implement this stuff, and argue about it, and generally BELIEVE that anything having to do with CS is either unpractical or is easily enough learned in 30 minutes of reading.
And then I have to work with these people, and manage them! They have no grasp of how much they simply don’t KNOW. And at some point, their knowledge simply ain’t gonna cut it. And they are going to argue with me, or write me off as a user of fancy computer science jargon. I mean, it’s just register allocation, right? How hard could it be? It’s only BSP tree optimization, let’s just check all the options!
So I am trying to combat this ignorance for practical, selfish reasons. Programmers need to understand the problems they work on. They need to understand when they are out of their depths, and its time to hit the books, or call someone who knows. Or reject that project, or bump up the cost and time estimate. At least map out the areas of your understanding, so you’ll know when you’re on treacherous ground.
The other reason is a matter of principle. Ignorance is pretty bad, and I reject mediocrity for its own sake.
In less fancy terms, if you are writing technical posts, get the technical details RIGHT! Isn’t that a given? But apparently I am an asshole for pointing it out 
For the person who asked, the reasons I read Jeff’s posts are two:
a) Jeff often finds interesting links. I sometimes only skim through what he writes, looking for the links.
b) On occasion like this, I have a chance to make my contribution to education. Maybe help some of the people who would otherwise be misinformed, by pointing out mistakes. People that some day I might work with. I’d rather their eyes don’t glaze over when I mention fancy computer science jargon.
@Swami: calling me an anonymous coward is fine, and perhaps far from the truth, but is also an ad hominem argument.