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No, Life Has Not Been Found In a Meteorite
The Bad Astronomer writes "News is going around the web that a scientist in the UK has found life (in the form of microscopic diatoms) in a meteorite, and has even published a paper about it. However, there are a lot of reasons to strongly doubt the claim. While the diatoms appear to be real, they are certainly from Earth. The meteorite itself, on the other hand, does not appear to be real. Many of the basic scientific steps and claims made in the paper are very shaky. Also, the scientist making the claim, N. C. Wickramasinghe, has made many fringe claims like this in the past with little or no evidence (such as the flu and SARS being viruses from space). To top it off, the website that published the paper, the Journal of Cosmology, has an interesting history of publishing fringe claims unsupported by strong evidence. All in all, this claim of life in a space rock is at best highly doubtful, and in reality almost certainly not true."
Incorrect.
"An ad hominem (Latin for "to the man"), short for argumentum ad hominem, is an argument made personally against an opponent instead of against their argument.[1] Ad hominem reasoning is normally described as an informal fallacy,[2][3][4] more precisely an irrelevance.[5]"
His argument is either valid or invalid but it's validity isn't related to his personal credibility. Attacks upon his character or credibility are irrelevant. "it's part of how we judge reliability of sources" He is a human, it is safe to conclude he isn't a reliable source. The same would be true if he were a solidly credentialed professor with 60 years of consistent publication. If one were asserting his was correct because of a positive history it would be another logical fallacy known as a plea to authority. If his data is bogus it won't be replicated. If his logic is faulty it should be dismissible with examination of nothing but his argument and premise.
At no point does it become valid logic to dismiss a sound argument on the basis of labeling someone a crackpot or dubious. It might be a valid personal screening criteria for whether or not you care to take the time to examine his argument that would hardly give you grounds for asserting to others that he is wrong which is what the submitter has done.