Homework is especially problematic on a number of STEM related stack exchange sites. There is a constant deluge of it on StackOverflow, Math, and Physics... and we get a bit of the spillover from StackOverflow.
The fundamental problems with trying to tack homework on to an existing stack exchange site are the combination of (what many see as) arbitrary constraints ('do this without using a for loop') and that the person asking the question isn't going to necessarily understand the answer.
Furthermore, students seem to have great difficulty searching and finding existing answers for their questions that they ask again and again and again and again and... well. That question gets asked a lot.
This existing knowledge base is the center of the of the Q&A format and it is key that people asking questions use that knowledge base and then ask a good question if its not there. Many homework problems fall into that category of missing what is there and not asking a good question.
Most people in Stack Overflow and Programmers.SE answering questions are not educators. We're posed with a problem and we look to solve it. We take shortcuts. We skip over things. We don't know what the educators are actually trying to teach. In many cases, for us (professionals in the work force) trying to help students, they will learn really bad habits that miss the target of what is trying to be taught.
Actually teaching someone requires a dense two way communication in most cases. Our answers are (should be) the quality of a good lecture. Thats not a two way communication. When a student is having trouble and has missed (the point of) the lecture, us, providing another lecture isn't going to help. What they need to do is go to some place that provides the means for two way communication. Office hours are the best option there. Failing that, a chat or discussion oriented site is probably a better option for working through the understandings and misunderstandings of the material.
I've helped people work through a number of homework issues in chat. The back and forth of explaining and re-explaining something when it wasn't understood the first time - and me actually getting the feedback of what is and isn't understood as I type it is key. Doing such a question as Q&A on the main site would have been tedious or a chameleon question that keeps morphing with the new understanding and gets re-asked again and again with edits and updates that leaves the resulting mess something that is so specific to that person asking that it becomes useless for the site as a whole.
As an aside, I will point out that there are some entire SE sites that are dedicated to specific courses (this appears to be a bit of a trial run to see if it works or not): http://cs50.stackexchange.com and http://edx-cs169-1x.stackexchange.com are two that I've stumbled across. Note that these are designed for asking for help about specific problems with well known (to the people answering) constraints. They still don't do the dense communication well though.
The Stack Exchange format is specially designed to try to avoid, hinder, and prohibit the back and forth and conversations one finds in forums. It does this to maintain the focus on Q&A, not discussions. I'd suggest giving A Group Is Its Own Worst Enemy a read. In particular:
4.) And, finally, you have to find a way to spare the group from scale. Scale alone kills conversations, because conversations require dense two-way conversations. In conversational contexts, Metcalfe's law is a drag. The fact that the amount of two-way connections you have to support goes up with the square of the users means that the density of conversation falls off very fast as the system scales even a little bit. You have to have some way to let users hang onto the less is more pattern, in order to keep associated with one another.
As to an Area 51 proposal for homework, I'd give Request for a homework Stack Exchange site a read. The proposal itself appears to have been deleted. You can get an idea of some bits about it on with this search. You might poke on Meta.StackExchange for more on why homework and SE's Q&A format don't work well (I'll warn you that you might get a few down votes if you try asking for such without being aware of the history to it on MSE though).