My law lecturers were variously keen observers of politics, literature, art, human nature and economics. One of the people I most admire as an essayist and thinker has three (three!) law degrees.
However, putting aside the exchange of anecdotes at twenty paces: you're absolutely right. In every profession there are people whose vision never rises above their own blinkered view of the universe.
I guess my point is that being intellectually parochial is ... well, it has drawbacks. Especially if you set out to explain why your profession is amazing and you have nothing whatever to compare it with except ... your profession.
Every time I wander out of my own field I first of all make a total arse of myself. But I always come back clutching something very useful. I never thought Olympic weightlifting would have given me useful life insights, it has. I never thought that learning muscular physiology would help me better understand software architecture, it has. I didn't think systems dynamics or fuzzy logic would upend my view of the world. They have. I didn't think that learning the basics of accounting would change the way I think about how to pick startup ideas, it definitely has.
And studying law, even though I dropped out because it made me unhappy compared to cutting code, gave me training in a model of thought that I still find tremendously useful.
Do you have evidence to back this up? Something more then anecdote?
You cannot know everything about every domain. There are people better than you at everything. The balance between specializing and diversifying depends on so many variables. This isn't something you can make a trite generalization about.
edit: And out of the professions I've experienced, the most widely diversified one is "I don't have the data to tell you."
Oh absolutely. No contest.
For example, regulatory laws must take into account political restrictions, economic theory and realities, and the goals and pragmatic realities and of the specific industry or industries being regulated. Criminal laws must do all that and take into account various socioeconomic factors. Tax law is a balance of economic theory, revenue generation, political restrictions, and pragmatic realities of accounting across thousands of industries.
Some other professions off the top of my head that can't "stick to their knitting": mathematicians, programmers, philosophers, psychologists and economists.
Even asking them things that their businesses depended on, like "What do you think will happen as patents on computer implemented inventions become significantly more popular?" and "If large-money companies start suing each other over these kinds of patents, do you think it will eventually cause significant scaling back in what is allowed?"
The answers I got told me that most couldn't even theorize/be visionary/plan about things absolutely critical to their current business//field.
Note: I was talking to people who were managing partners/etc, who were making significant money due to the upswing in patenting software. They were also not stupid people, just, AFAICT, bad at business. Most lawyers i've met are actually very bad at running businesses, but i'll save these stories for another topic.