It may have just been that this was only really big news in India, and as a result (nearly) everyone who commented had an emotional stake in the argument. Or, also likely, I just had trouble understanding everything they said and alluded to, as I am unfamiliar with the people, books, and myths they talked about.
Anyhow, here are 3 comments which I felt were particularly not credible.
A
1.
This comment doesn't seem to be expressing too much, but I can assume base on the author's position that he hopes for this aeroplane discovery to be true for whatever reason (whether it's because it just seems cool, or he's patriotic, and wants India to have this scientific discovery under its belt)
2.
I can't really tell what beliefs this person may hold, beyond that India had spaceships 7000 years ago.
With this comment, the most immediate hit to the comment's credibility is the grammar and spelling. However, I think to some extent I should ignore it, because India has so many languages, and English, though widespread, isn't easy, and I feel I can safely assume GCM, here, just doesn't have it 'down-pat' yet.
However, he does us "n" instead of "and" which shows me that he isn't even trying with some of it, which loses him some credibility.
Apart from that, it seems to me that he tries to take the high road, not even trying to explain, because he assumes that the opposition's arrogance makes it not worth-it to make his point. As a result, his point is not well-supported.
B
1.
This comment definitely expresses some fear that India (I assume his home country) may lose credibility in the scientific community as a result of the speakers at the ISC.
2.
I can also assume that he is Hindu, which adds to his outrage at these people with whom he doesn't want to be grouped together. Unfortunately, it also shows that he more emotional stake in the argument.
3.
This example is on the more-credible side of the spectrum, But he resorts to calling RSS chumps, and saying that all Indians should say Rss doesn't represent them, even though, I'm sure it does represent quite a few at least.
C
1.
Much like the first comment, this one doesn't really express any fear, but a sense of nationalism. He counts this proposed achievement of ancient space-planes as partially his own, which, if someone tries to disprove it, could make him anxious about his and his country's standing. essentially, he, like so many other commenters, has a strong personal attachment to the argument.
2.
This person directly shows his belief that the ancient of his country attained space travel, but also that others only disagree because of their own nationalism; he says they are jealous of his country.
3.
Just like almost every other comment, this one shows personal stake in the argument. He also implies that jealousy is the sole reason people criticize this proposal. He doesn't even seem to consider that people criticize it because it just seems absurd, and requires some factual support.
Reflection:
After reading Charles' and Clayton's blogs, I realized that one thing that is very important to consider when analyzing comments is to not decide whether it is good or bad at the start. Clayton did a very good job of this, as he didn't let the fact that a comment was, for example, in the non-credible group cloud his analysis. He still noted the good parts of the comment that were reasonable.
Likewise, any credible comment can have flaws that make it not perfectly credible, just good enough.