I think it is bad policy to start a stackexchange community by ostracizing those who want to write in some dialect. Well understood in the Arabic world one writes in MSA, but all Arabs do live in a "dialectal" environment, foreigners travelling in the Arabic world do have to deal with dialects, and this is reason enough for useful questions about dialects to be raised and answered. And sometimes the best way of formulating a question about dialect, is in the dialect itself.

IMHO one should let people write in (and care about) whatever form of Arabic they want (MSA or some dialect, written in Arabic script or some transliteration) as long as they tag their question properly as concerning (or being written in) a specific dialect. And time will show whether the community will tend to be MSA-only, or rather dialectal, or both.

After all, you can not evacuate the fact that every native Arabic speaker also speaks at least one dialect, and that this dialect may be much more important than MSA for him/her in his/her daily life. And *dialects make Arabic culture richer*, they should not be considered as a "necessary evil" or as a "handicap", as some MSA-purists do consider them.

Otherwise you should consider renaming the community into "Modern Standard Arabic Language" as to avoid misunderstandings.