But what about asking why 4E doesn't do something well when you already know the answer or that the answer is self-evident?
It is still a valid critique of the design, depending on context.
For instance, if Game X had always had an element in it that was fairly popular or was very good at simulating a particular aspect of the game's genre, and the newest edition eliminated that element, questioning that element's elimination is completely valid. Take this post that showed up while I was writing mine:
Take for example, simulationism. 4E has made a specific design choice to throw any hint of simulationism completely out of the game, and that is the answer.
Its a common thing to see people talking about why a particular game doesn't do something well when another game does, and a common response to say "Then go play that other game." That being the case, players of the previous edition are perfectly justified in asking why remove an element from a game when you could design a different one.
Asking why Game X didn't do something well when it is something completely new element added to the game's new edition is also valid, since you'd expect that flaw to become evident during playtest.
Wondering why Game X doesn't do something well regarding something that's a port from a game in another genre raises the question of the justification for its inclusion.
OTOH, wondering why Game X doesn't do something well that has absolutely nothing to do with Game X in ANY iteration...well, that's possibly a sign of insanity.
Now, the fact is, asking such a question may be unanswerable by anyone who didn't actually work on the game's design...but its still a valid critique.
But trying to elicit the obvious or self-evident answer is a valid rhetorical technique. Sometimes it helps remind persons of the facts (something that can be lost or ignored in a vigorous debate)- a technique called "refocusing". Sometimes its used to have your debate opponent paint himself into a corner.
And sometimes,
sometimes it helps to expose a troll...on
either side of the debate (the asker or the answerer).