If the community had a consensus on behaviour, and a semi-private messaging system, community members with some standing could try countering rudeness by sending the poster little reminders of how such-and-such comment runs counter to the behaviour/culture/atmosphere being maintained for the forum.  In some cases, posting an additional comment would suffice, but at the cost of having such comments contribute to the noise level.

Here is an idea, assuming that Gerry's suggestion or something like it is generally agreed upon: for every such "do your own homework" comment, send a tsk-tsk to the commenter.  A tsk-tsk is either a follow up comment posted to the same question which links to this meta question (or appropriate section within this question), e.g.  "Tsk @Gerry, https://meta.mathoverflow.net/questions/1107", or it is a comment
posted in this question with enough context for the commenter to take action, e.g. "Really @Gerhard, in http://mathoverflow.net/questions/abcdef you could reflect community ideals by commenting as Gerry suggests above, or not commenting at all."  The point of this convention is to move noise away from the questions and toward meta.  Also, some rules should be followed, the most basic one being that if the commenter fixes the associated problem, the tsk be removed by the tsk-er or moderator.

If such a community-correcting system is implemented, I intend to keep a count of how many tsks I receive.

Gerhard "Of Course, Not For Signatures" Paseman, 2013.10.29