You won't crash on the field because the vis has dropped.
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Totally agree, but ...... I may be tempted to start an approach if I'm not told that the vis. / RVR has dropped, and when reaching MDA commence an overshoot ( Go Around ! ) and ....... then find that we have another problem, or issue, that creates a scenario that results in an accident, whereas if I had never even considered making an approach - having been told that the airfield was below minima - I might well be at a different height, in another place, where the second problem would not be a problem, or could more easily be dealt with.
One could hypothesise for ever, but a crew can only make a decision based on the facts presented to them, and if they are told that the RVR is above minima, why wouldn't they start an approach - all else being equal - why give pilots false info ?
No pilot deliberately flies into the ground, or mountain, he flies into the ground because he is convinced it isn't there, from clues presented to him from a variety of sources, some mechanical, some audio, some electronic, some visual, some from other humans, and if those clues are false he makes the wrong decision - and is usually not around to explain, so the easy answer for those really at fault ( maybe ) is to blame him / her.