Legislation is written contrariwise, which can seem baffling to programmers unfamiliar with the system.
It doesn't seem to be like this in the US. If you look at laws in the US, they try to define every word and every situation with a lot of cases. Vagueness seems to be avoided, and I'd say it actually doesn't seem too unfamiliar to programmers if used to the jargon
As for vagueness, the issue has more to do with the scope. To me, as a citizen, the expanse of a given law is over the union of every possible interpretation of it that can be made by a reasonable person.
The more vague the language in a given law, the larger the scope for interpretation; the more specific and descriptive the language, the more restricted the scope.
It seems like an abdication of responsibility by duly elected legislators to leave the interpretation of the bounds of a vague law onto a far-removed, indirectly-elected judiciary, rather than passing specific laws defining those bounds more carefully from the get go. Why not just create a single law "Enforce good. Punish evil.", and leave it to the courts to implement?
As for why this uproar happens specifically on topics regarding the internet, the audience here on HN has a larger interest in everything to do with it compared to other issues. I do think that the same level of caution should be applied w.r.t. any and all vague laws, regardless of the topic.
The real question is why people take the it's-very-common approach to belittle people's concerns.