@shazow.eth
Some definitely comes from insecurity (as others said), but IMO the other half comes from overfitting from expertise.
Common HN commentator: someone Very Smart thinks new thing is dumb or obviously a scam. Anything crypto-related for example, like the Classic Smart Finance Person, or the Classic Smart Distributed Systems Person. Anything cryptography-related was another classic example that predates crypto, Classic Smart Cryptographer is very upset that someone dares attempt to improve on usability of Very Serious encryption workflow.