Decent below MDA, Legal?

Greg Esres wrote:

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In dismissing the 91.155(a) charge and affirming a 90-day
suspension, the law judge relied on our decision in Administrator
v. Vance, 5 NTSB 1037 (1986), wherein we held that an instrument-rated
pilot's takeoff -- without an ATC clearance -- into
uncontrolled airspace in instrument meteorological conditions
(IMC) was technically legal under the predecessor section to
section 91.155(a), but was nonetheless careless, in violation of
the predecessor to section 91.13(a).
-------------snip---------------

This has some interesting implications. Obviously, what's legal and what's
safe are not the same. But how is "safe" determined? A take-off at full
gross on a runway with *just* enough room to get off is legal. Is it safe?
More importantly, could one be cited for "careless and reckless" for doing
so?

My concern is that this can be used rather arbitrarily.

- Andrew