If, like me, you are extremely argumentative, and enjoy debating various things, you might be tempted to venture onto a left-wing blog and make some comments. After all, it isn't as interesting to argue with people who already generally agree with you. When I comment on left-wing blogs, I try to restrict myself to very specific points, knowing that I am dealing with people who are operating under radically different fundamental assumptions. Since many on the left live in an echo chamber, I think it can be useful to point out that others do not share their views, and to do so in as calm and logical a fashion as possible.
When it comes to atheist blogs, I expect that most atheists value logical reasoning, since even leftist atheists often apply excellent logical skills to debunk religious arguments. Sometimes you can generate a reasonable debate, even if the ultimate result is to agree to disagree. But then there are times when you get the usual left-wing responses to anyone that dares challenge their assumptions: an onslaught of strawmen, intellectual dishonesty, false analogies, ad hominem attacks, and a general lack of reading comprehension. For a prime example of what I'm talking about, see this post and the comment thread.