Should we forbid Unicode characters completely/partially/or not at all, in the hope to prevent abuse and possible vandalisms on SO?
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Should it be disallowed?
Banning Unicode would make globalization of the sites impossible, so at best this could only be temporary.
Using a white- or blacklist for allowed/disallowed characters is extremely problematic.
The community handles spam on its own very quickly either by editing it out, or flagging.
As a potential abuse of the system, posts with this content can be seen by, or reported to, moderators who can penalty-box users as appropriate for repeated offences.
Z̵̬̮̫̞̪͖͔̖ͩ͐̓͌̓̍ͬA̝̺̗̜̯̱ͣ͐͆́Ḽ̷͚̼̠̘͎̈̀̂̋ͅĜ̩͚̲͕ͯ̚͢͡Ò̷̜̼̲̻̑͘͢ ̬̤̭̗̲̗̺ͫ͋͝W̵͈͔͎̞̠̲̯͌̌̾́I͔͓ͪͥ̆ͩͬ̀ͫ͑̐͘͠Ḷ̤͉̓͐͐̎̒́L̖̟ͤ̌̅ͬ̂̀̕ ̟̥̣̼̥͒ͧͮͬ͒̋ͥ͒͝C̜̥̱̘̗͓͍͔̓̒ͭ͐̇͜O̵̙̰̖͓͐̇̑̋ͩ̄͡M͊ͩ͆͊͏̰̫̭̳̼̠͎͡͝E̿͆͏̞͞ ̧̛̰͚̜̘̞̫̹͉̈́̽͒͒̂͐ͮ͋̍͘ ̧̞̙̗̪̳̍̐̀̌ͨ͜D̗̼̾̾O̘̠̓ͯ̀ͬ ̛̼̩̮͔ͣ̊͒̿̏ͭ̆N͇̥̤̯̮̣̖̖ͣ̓ͫͨÔ̴̢̯̼͕̮̺̰̗̓ͤͯͅT̘̈́̎͐̃ ̸̨͉̩̟̇͂͗͢À͉̜̝̥̝͎͉̗̔ͦ̊̓͐͟N̫͙͙̙͇̯͙͕̏͌ͥͤͥͦ͐͒̃̕G̣͚̖͚̱͎ͣ̓͛̎ͭ̄́E̹̝̣͚̹̗̻͉ͪR͍̗͙̹͑̓͟ ̫̥̤̖̳̼͕̯ͪͮ̌ͮͦ͡Zͩ͊͐̍́̋͏͚̬̦͕̫̙̩A̷͕̗̘̬͍͛̍ͭͣͫͭ̚͢ͅL̢̖̠̫̍ͦ͂̂ͭ̄͛G̖̙͙͓̺ͨ̆ͬO̵̹̫͚͉͈̣͖̔͗ͮ
Of course we should allow freakin' unicode.
Unicode support was such a big deal 10 years ago. Removing support represents an enormous step backwards, for no good reason. How can you have a programming site that doesn't even support Unicode in 2011?
This is an awful question the way it is stated, if anything an ASCII diagramming toolkit should be created to create ASCII tables and the like, for use in ASCII diagrams. Plus it would break this answer.