user1578: Most users of this site subscribe to the evolutionary origin of species as opposed to intelligent design - but some of them seem to operate from a wrong mental model of evolution which supposes it should act like an intelligent designer.
This is evident in questions whose answer can be generalized as "Because there was no natural selection for/against that". The newest example which prompts this question is Why do teeth decay of sugar?, but there are other examples, such as The skin color of bonobos, How does Oedipus complex fit in the evolutionary theory? (OK, this one has other problems, but it is still a good example, because the OP assumed Oedipus exists) and Why have whales and dolphins not evolved to have gills?. Basically, somebody thinks "Wow, a species would have it better if it had/didn't have trait X" and asks "How come trait X evolved/didn't evolve when it would have been so awesome to not have it/have it?".
I agree that this type of question is not flat-out wrong for the site because of the faulty assumption, as discussed in Voting to close a question as off-topic because it is based on a faulty presupposition. But answering each of them with the same explanation of how evolution doesn't work would become tedious as these questions grow in numbers. Also, it goes against StackExchange's goal of making information findable, because the general knowledge is hidden under a very specific question.
Is there a solution for making this easier on both the people who want to answer and the people who want to learn? Maybe making a canonical question to which we link from any new question which makes us think the author does not realize that evolution is not about adding cool design elements to animals?

user13072: I think that having a single consistent high-quality internet resource to which we can direct these people would be extremely useful. The Understanding Evolution project at UC Berkeley would be my choice. They have both a useful tutorial Evolution 101 for those who want to grasp the basics of evolutionary biology, and a nicely done FAQ on misconceptions about evolutionary biology. 
For the particular misconceptions that you describe here, I'd recommend some combination of : (1) MISCONCEPTION: Natural selection produces organisms perfectly suited to their environments. and (2) MISCONCEPTION: All traits of organisms are adaptations.

1578: <p>Most users of this site subscribe to the evolutionary origin of species as opposed to intelligent design - but some of them seem to operate from a wrong mental model of evolution which supposes it should act like an intelligent designer.</p>
<p>This is evident in questions whose answer can be generalized as &quot;Because there was no natural selection for/against that&quot;. The newest example which prompts this question is <a href="https://biology.stackexchange.com/questions/34135/why-do-teeth-decay-of-sugar">Why do teeth decay of sugar?</a>, but there are other examples, such as <a href="https://biology.stackexchange.com/questions/26217/the-skin-color-of-bonobos">The skin color of bonobos</a>, <a href="https://biology.stackexchange.com/questions/17235/how-does-oedipus-complex-fit-in-the-evolutionary-theory">How does Oedipus complex fit in the evolutionary theory?</a> (OK, this one has other problems, but it is still a good example, because the OP assumed Oedipus exists) and <a href="https://biology.stackexchange.com/questions/29846/why-have-whales-and-dolphins-not-evolved-to-have-gills">Why have whales and dolphins not evolved to have gills?</a>. Basically, somebody thinks &quot;Wow, a species would have it better if it had/didn't have trait X&quot; and asks &quot;How come trait X evolved/didn't evolve when it would have been so awesome to not have it/have it?&quot;.</p>
<p>I agree that this type of question is not flat-out wrong for the site because of the faulty assumption, as discussed in <a href="https://biology.meta.stackexchange.com/questions/2961/voting-to-close-a-question-as-off-topic-because-it-is-based-on-a-faulty-presuppo">Voting to close a question as off-topic because it is based on a faulty presupposition</a>. But answering each of them with the same explanation of how evolution doesn't work would become tedious as these questions grow in numbers. Also, it goes against StackExchange's goal of making information findable, because the general knowledge is hidden under a very specific question.</p>
<p>Is there a solution for making this easier on both the people who want to answer and the people who want to learn? Maybe making a canonical question to which we link from any new question which makes us think the author does not realize that evolution is not about adding cool design elements to animals?</p>
 13072: <p>I think that having a single consistent high-quality internet resource to which we can direct these people would be extremely useful. The <a href="http://evolution.berkeley.edu/evolibrary/home.php" rel="nofollow">Understanding Evolution</a> project at UC Berkeley would be my choice. They have both a useful tutorial <a href="http://evolution.berkeley.edu/evolibrary/article/evo_01" rel="nofollow">Evolution 101</a> for those who want to grasp the basics of evolutionary biology, and a nicely done FAQ on <a href="http://evolution.berkeley.edu/evolibrary/misconceptions_faq.php" rel="nofollow">misconceptions about evolutionary biology</a>. </p>

<p>For the particular misconceptions that you describe here, I'd recommend some combination of : (1) <a href="http://evolution.berkeley.edu/evolibrary/misconceptions_faq.php#b7" rel="nofollow">MISCONCEPTION: Natural selection produces organisms perfectly suited to their environments.</a> and (2) <a href="http://evolution.berkeley.edu/evolibrary/misconceptions_faq.php#b8" rel="nofollow">MISCONCEPTION: All traits of organisms are adaptations</a>.</p>
