That's an argument from authority, plain and simple. Whether or not you know anything about lisp, your comments about it should be judged on their merits alone. If you truly don't know what you're talking about, it should be apparent to those who do know what they're talking about.
A master and a novice might sometimes come to the same conclusions, but seldom because they followed the same thought process. And I sure hope you aren't upmodding posts that don't share any of the thought process behind what they're saying, the reasons why they conclude what they conclude.
Knowing context might make a post more valuable, in the sense that you understand better how it fits into the wider world, but it won't generally make the content any smarter, more valuable, or more correct.
That's an argument from authority, plain and simple.
Have you ever wondered why, thousands of years after the ancient Greek experts on rhetoric noted the existence of the "argument from authority" fallacy, we're still awash in authorities? Are we all hopelessly stupid, that we cannot learn to avoid this mistake?
Perhaps. But another problem is that argument from authority is almost never "plain and simple". There's no bright shining line between an argument from authority and an argument based on an overwhelming accumulation of evidence. At some point it comes down to a judgement call.
Suppose a mythical person named Graeme Paul (let's call him "GP" for short) arrived here on news.YC and submitted a one-sentence essay: "Most of the smart programmers that I've met would rather work in Lisp than in Java." My reaction to this would be straightforward: GP is a troll. A very boring troll.
Now let's suppose that GP's post is a bit longer: It begins with his autobiography, in which he talks about his young days as a programmer, and his first encounter with Lisp, and describes the various things he has built in both Lisp and Java. He then gives a detailed, prioritized breakdown of the design of the Java language, comparing Java's features with analogous features in two or three different varieties of Lisp. During this discussion, it becomes clear that GP understands the technical compromises, that he's seen the insides of many real-world Lisp and Java projects, and that he's a gifted explainer. Finally, GP wraps up by summarizing his personal discussions with the designers of Scheme, Java, Ruby, and C.
GP is no longer a troll. He's now making a serious and detailed argument, with many facets, that goes on for pages and pages. He may still be wrong -- history is replete with examples of obsessed experts who were wrong -- but he's got a much better argument.
Now let's suppose that, instead of typing all that information in one monolithic 193-page post, GP spread it out over several hundred blog posts and news.YC comments, posted over several years. At the end of that time, he comes along with a one-sentence post in some language-war thread: "Most of the smart programmers that I've met would rather work in Lisp than in Java."
Because this single sentence is a summary of a long-standing, well-established series of arguments from GP, I might (in the right context) mod it up. Then, no doubt, I would be accused of "not judging this sentence on its merits alone".
The puzzle question here is: Since GP's huge body of published work arguably establishes him as "an authority", is my deference to GP an "argument from authority"? Well, if I've never read any of GP's work but I upmod him anyway because he's famous, the answer is "yes". If I've read GP's earlier work and know that it backs up his latest claim, the answer is "no". Can you, gentle reader, tell the difference between these two cases? Not unless you know my reputation, and/or ask me to provide up to a dozen pages of rationale and clarification.
And there's a huge grey area: If I've read GP's writings on Lisp, and he comes out with a statement about (e.g.) Ruby, how shall I value his expertise when weighing the credibility of his latest statement? It's a judgement call.
Are we all hopelessly stupid, that we cannot learn to avoid this mistake?
Many of us are, though I wouldn't say it is necessarily only stupid people who do it.
I consider it a good principle that the words in a reply in forums like this stand by themselves. If you or pg or anyone else wants to say something about lisp, you got to back it up. If you have already backed it up in "several hundred blog posts and news.YC comments, posted over several years", it should be easy for you to reference some of this material in support of your views.
You saying that the exact same argument, presented word-for-word the same, is not worth as much as the same thing when it comes out of an authority's keyboard, is an appeal to authority. However, if this other person has already defended this view, all he has to do is reference it to make the post worth more. But then the posts aren't word-for-word identical. Then one contains a reference to a justification and one doesn't.
Your example involves a question of how much to trust a person. This is one of the cases where it matters who's making the comment. It's a straightforward question of whether you want to trust that the person who says "Most of the smart programmers that I've met would rather work in Lisp than in Java" is speaking the truth or not, and it's clear that a habitual liar isn't as trustworthy as someone known for their honesty. It's not even an argument, it's just a truth claim.
However, the moment it becomes an argument (e.g., "lisp is better than java"), trusting it on authority becomes a fallacy. If Paul Graham wrote, "Lisp rocks", his comment is not worth any more than your comment if you wrote the same. But if he wrote, "Lisp rocks, for reasons I have detailed in this essay here: <...>", it would be worth more. But then it would no longer be "exactly the same words".
A master and a novice might sometimes come to the same conclusions, but seldom because they followed the same thought process. And I sure hope you aren't upmodding posts that don't share any of the thought process behind what they're saying, the reasons why they conclude what they conclude.
Knowing context might make a post more valuable, in the sense that you understand better how it fits into the wider world, but it won't generally make the content any smarter, more valuable, or more correct.