As of the last database dump, there were 9831 users who had posted on MO. Of those, 6236 posted a question before posting any answers. Of those first questions, 1604 of them were closed (about 26% versus the global average of about 11%).
So first questions account for about 3/5 of all closed questions. On the other hand, if you ignore users who start out by asking a question that gets closed, it's still true that most users first start using MO by asking a question. Offhand, I happen to remember that this includes desirable-but-not-very-active users Michael Freedman and Vaughan Jones. I think this argues strongly against a minimum reputation for asking questions.
]]>Such a decision would slowly kill the site, since it would create an imbalance in the number of people with research-level questions and those with research-level answers. Then, when those answerers find no questions to answer, they drift away and don't come back.
]]>I can vividly remember various somewhat heated discussion on question, but in very few cases would the questioner have been impeded from asking the question by your or any other of the suggested mechanisms (in some cases technically by yours, but the questioner typically could have answered something easily and I doubt they'd been convinced in the process not to ask the question).
To me all these suggested measures would at best remove something that I considered a very minor problem. Somebody just asked a group-theory excercise, so what? Costed me ten seconds to vote to close; if I'd been the first on the question perhaps a minute to type the closing message. If I would not want to deal with this at all I'd just read question that 'survive' for a couple of hours.
But the really more problematic situations would not be avoided, since the 'problem' is that the opinions among frequent users are split.
]]>There were suggestion in a similar spirit see here and here, for example. In particular, see grp's suggestion of a two-tier system in the second thread [however, this is an idea feasible only assuming somebody would develop a custom version of the software for MO; and indeed came about in the context of such a discussuion].
Finally my personal opinion, assuming for the sake of argument it would be possible: I am not at all sure I'd be in favor of it (I say this as somebody not having asked a single question, but having given close to 100 answers). For example, a side-effect could be creating low-quality/redundant answer given for the sole purpose of 'finding' some initial up-vote. And, there are some users that asked numerous legitimate question before ever gving an answer, some never gave an answer so far. Or, I would also not have liked to somehow be forced to ask something first before being able to answer (could also suggest this, after all a low-quality answer can be more harmful than a low-quality question).
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