I don't think it's anywhere near that complicated. People argue about languages because languages become part of their identity: It's common to think of oneself as for example a "Lisp Programmer". And if a language is part of your identity than people saying less than amazing things about that language feels like an attack on you personally, and very quickly the discussion devolves into an argument that has nothing in particular to do with the actual languages as such.
The problem is one of identity. We will protect anything that we attach to our identity because we perceive any attack on it as an attack on us. To have intelligent, unemotional conversations that has to be decoupled.
In general it can lead to problems if we map our identity externally - whether to a programming language, or something else - of course this is easier to preach than to practice.
Can you point out some things that don't become part of people's identity? My experience is that anything that someone spends more than a tiny amount of time with immediately starts becoming part of who they are.
The boundary of our self is constantly spreading outwards onto the things around us. Seems to be part of human nature.
Psychologists have a concept known as "self-complexity" (wiki it). Basically, it's our view of ourselves, in terms of the many attributes, relationships, skills, deficiencies, etc. we possess. Someone who thinks of themselves in broad terms, filling many roles and with many aspects, is said to have a high self-complexity. Someone who thinks of themselves in terms of only a single aspect has low self-complexity. Think of "I'm a world-class kernel C hacker" vs. "I'm an awesome C programmer" vs. "I'm a good programmer" vs. "I'm a decent human being".
So no, it's not bad for new activities to become part of your identity. It can be bad for them to become your whole identity, because it leaves you really vulnerable to outside attacks on your self-conception.
(On a side note, it seems to me that a lot of the Silicon Valley startup mythology is focused on encouraging low self-complexity and an obsessive focus on external success. Now that I re-read some of PG's early essays, several of them seem actively harmful to one's mental health. The YC application used to ask you "How are you an 'animal'?", in reference to an early essay where he suggested that successful startup founders often act like caged animals - as if denying your humanity is "success".)
Generally really like your post, but I have to correct you about PG's essay.
It's people who work at normal jobs that he calls caged animals, and founders are the wild animals.
"In fact, getting a normal job may actually make you less able to start a startup, by turning you into a tame animal who thinks he needs an office to work in and a product manager to tell him what software to write."
"One of the best tricks I learned during our startup was a rule for deciding who to hire. Could you describe the person as an animal? It might be hard to translate that into another language, but I think everyone in the US knows what it means. It means someone who takes their work a little too seriously; someone who does what they do so well that they pass right through professional and cross over into obsessive."
I think it's because we invest so much time and energy working with them. Most humans can't do that without becoming attached.
Once you identify with something it becomes difficult to be objective about it. So discourse about technical tools is mostly emotion, however rational it pretends to be. That's why the core debates never end.
By the way, you can add version control systems to your list.