I am unhappy with the current situation of "I left my food out, is it safe to eat" questions. The closing as a duplicate after the first canonical question was created reduced the influx, but they did not disappear, and currently they seem to be on the rise.
These questions are not good for us. Our site is created to cater for people trying to reach a rational decision after weighing the relevant information. These questions do not come from people trying to make a rational decision, so our system fails in handling them. We should close them before they do damage to the OP, to our community and to our signal-to-noise ratio.
Neither answering them nor closing them as duplicates is a good solution. They require a very general rule to be applied in a uniform manner to a specific case (which interests nobody but the asker). Imagine if math.stackexchange was flooded by questions asking "How much is 4 + 7", "How much is 9 + 3" and so on. It is ridiculous to answer them all. On the other hand, they are not really a duplicate of the canonical questions we created. The canonical questions describe a rule, but an one can only arrive at the answer of the specific questions after applying the rule.
What we want to do with our site is help people solve a problem. Is the OP's problem "I don't know how to correctly store food"? The wording of most of them leads me to believe that it isn't. They tend to recognize that they did something wrong when they forgot their groceries overnight in the car. Their problem is not missing knowledge, it is cognitive dissonance. "I want to eat this, because [I spent so much money on it | I feel that the normal food safety rules are too paranoid | I don't believe I will get sick if I eat it ], but I am aware that I hurt the rules of proper storage. Please give me absolution and tell me that I may eat it." We cannot solve this problem by linking to a rule which says "if you did not store it like this, throw it out". First, the people who ask already seem to know that their practice is unsafe (we could only once or twice confirm that the food is within limits). Second, I doubt that they have the motivation to read through a long explanation which requires interpretation for their special case - humans are known for muddling through, confirmation bias, and other tendencies which would make them avoid reading the question to which we sent them.
The way I have been handling this until now was to close the question with a link to the canonical one, but also clearly give the actual answer ("No, it is not safe, throw it out") in the comment I leave before closing. I am not sure that this is helping the OP; I am sure that closing the question without such a mention will not help any. When they are looking for an explanation for their feeling that their case is an exception to the rule, citing the rule at them again does not change their feeling. These questions don't help the next asker, because they again feel that their situation is special. Anybody thought about how these first-time posters find our site? I just googled "I left meat out is it still good", and we are the third hit, with the question Why is it dangerous to eat meat which has been left out and then cooked?. If these people find this (or one of the old closed questions) with their search and still ask their own question, then they obviously won't change their opinion after seeing the old closed questions and the answer leading to the canonical question. And of course, these questions do not have value for us who handle them. They are just annoying. And at last, if we don't close the questions quickly enough, there is the chance that somebody will answer on the lines of "I ate stinky meat once and nothing happened, you will be alright", which is dangerous.
So I agree with Aaronut that the current situation of closing them as duplicates does not work well, and that a custom closing reason is the next best thing. We could word the reason for example as
Unsafe food storage - This question concerns the safety
of consuming food which the OP thinks has been stored
unsafely. We take it as undebatable fact that food which has been stored
under improper conditions should be discarded. The rules under which food
is considered properly stored are determined by legislature; we have a
short write-up here<links to our canonical questions>.
This requires the same amount of work for closing per question. But it tells the guilty OP seeking absolution that he/she won't find it here. It still contains the link to proper food safety instructions for those who want to read them. And it removes the ambiguity of closing them as duplicates. I hope that in the future, people who find a question closed with such a text will be more likely to refrain from posting a new question.