You can just deliver the counterpoint, explanaining how you think the parent was mistaken, without the personal insult. “The key point this comment fails to recognise is [useful new info]” might work well.
Thanks Tom, I felt bad making the retort as well as I like HN to be a happy place. For the record, I am majored in finance, mathematics and cryptography well before these things were linked. I discussed Bitcoin with Hal Varian in 2011 and staked our differing positions. It may be too early to call, but Bitcoin seems quite successful so far, and has served me well. I prefer not to rely on my credentials to make a point about economics since this is a logical fallacy.
