As far as that particular Wikipedia thing: I think a lot of people really liked the design, and most of them clicked the upvote. On the other hand, most of the people who didn't like it couldn't downvote so they left comments instead.
So part of the hostility you notice might just be the fact that they took on Wikipedia and really put themselves out there, so it was a controversial post. And HN needs to fix the downvote thing (there I go being negative again).
One other thing is that you have people with really different backgrounds coming to Hacker News. Some people are like me and have a lot of coding experience including, for example, enterprise(y) application programming. Other people have much more experience in marketing and/or graphic design and/or UX/UI.
This might just be another example of me having a bad life, but there also might actually be a bit of pent up resentment between UX/UI designer people and coders in general. I will be too honest as usual and elaborate.
Basically, what it seems like from my own programmer perspective is that the people doing the software UI design in Photoshop or whatever think that they know better how to build software than me and therefore are placing themselves over me in the project decision making, even though they have written very little (or zero) code. That sort of misplaced disrespect could possibly sometimes make a person feel righteously hostile. Of course, I do realize that UX is its own field with knowledge that isn't automatically absorbed in the process of coding, but that doesn't really change the situation between coders and UX designers.