There's a fair amount of IRC channels which are nice (and where that's enforced). IRC is a technology, not an ideology, just like the WWW that underpins HN.
Yes, I agree that it's not all IRC channels, but you can see from the average bash.org quote how 'the social crowd' feels about this kind of talk.
WWW is a hypertext transport protocol, so it's not really like IRC at all. IRC is a group communications platform, and when you compare it to every other group communications platform, it's obvious it has a very particular culture. Part of that is inherent to the technical design of the protocol and its admin features. But mainly it's how humans interact in groups, and the features of the protocol being used by that nature, that shifts expected behavior.
The only things I can think of to compare IRC to is YouTube and Xbox Live voice chat. Short messages that are often a running commentary on some subject, which can devolve into unrelated argument, and is often filled with hateful and insulting diatribe. Anonymity preserves the behavior, and the lack of down-moderation of these comments, along with a total lack of consequence, means people get to say whatever they like. And often people have some pretty fucked up things to say.
In IRC's case, the technology can actually encourage the behavior because the ops decide what is acceptable or not. If the ops condone hate speech, it becomes acceptable culture. And due to the 24/7 nature of IRC, there's little way other than bots to monitor a channel all the time. You're right that the technology itself is not the main factor in how people behave using it, but human nature itself - when run amok - can often result in negative behavior. So IRC is a shithole not because of the technology, but because of people.