I did not plan to run any of the Twin Cities races. But to stir the pot...if I HAD registered for one of these races, it would've been because I was expecting cool to maybe moderate temperatures and would not have trained for hot temperatures. As a 5 - 6 hr marathoner, looking at a T+D of 86 + 66 = 152 at 1pm...I would not have made this. If I had tried to run at race pace, even with a starting T+D of 128, I would have been in serious trouble. If there wasn't much shade, then it would have been even worse.
I am affected by heat and humidity much more than others, and I know that about myself, so hopefully I personally would have given up any time goals and been very conservative. I've had three marathons turn into death marches because the temperatures got into the 70s F (and I was not the only one suffering). But there are lots of other people who would have been much more adversely affected than they expected.
I can definitely see why people are very disappointed not to do the race, but I do think it was a very responsible decision. It would have been pretty dangerous and it's a good point others mentioned that they would have needed far more hydration supplies, medical supplies, volunteers, and medical folks than they probably had ready to go.
I haven't paid enough attention to the timeline of when they made the decision and announced it, but a late decision for safety is better than not making that decision. If the race had been held and they had a catastrophic number of people with heat stroke, aid stations ran out of liquids and ice, medical stations were overwhelmed, etc. etc., and it came out that they thought about canceling but didn't because it was only X hours ahead of time, how would that have played?