Looks like the majority thinks no one was at fault. I feel the same way, FWIW. You flies your plane, you takes your chances. Someone back a page or two thought that "employing a spotter" was a bit extreme. Well, maybe 'paying' a spotter might be a bit much, 'using' a spotter is part and parcel one of the best preventions possible for mid-airs. When you're flying, your complete attention is (and should be) on YOUR plane and what you're doing with it. The spotter's only job is to watch out for other planes and their location and to warn his pilot when there's a conflict brewing over being in the same spot at the same time; allowing the pilot to make the decision of where to go to stay out of harm's way., based on what he can't otherwise see.
Of course, the possibilities of collision multiply exponentially with the increasing number of planes in the air, and the individual pilot has to make his own decision whether his will make too many for safe flying (safe for HIM, as obviously, his concern will be for his own plane more than any other). Also, the pilot needs to consider WHAT is already flying, in terms of whether they are just trainer types flying the pattern, 3-D'ers doing their thing, or warbirds doing low, fast passes, etc, and then deciding if his own flying style will 'disturb the mix'. I think the "Yugo at Daytona" analogy was apt, much the same as riding a bicycle in a motorcycle race would be
If the scenario was such that I saw a bunch of trainers and/or pattern planes (bunch defined as 2 or more) already flying while I was prepping my big expensive (or not so big, and inexpensive) warbird for flight, I personally would be inclined to wait for somebody to land before flying my plane. Conversely, if I saw several warbirds mock dogfighting or just making fast passes and chandelles, I'd also hesitate to take up my 3-D plane and hover, or my pattern plane and practice my routine. If I was already flying and saw someone take off (my spotter told me so, plus the other pilot called out his intentions to take off), I'd probably land as soon as reasonable because A-- the other plane might become a hazard due to its different flying style, and B-- I'm not familiar with the other pilot's ability to stay out of the way, or C-- I AM familiar with the other pilot's ability to not stay out of the way
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It all boils down to making a choice based on experience, or lack therof, and then accepting whatever happens later without saying it's the other guy's fault exclusively.