It's quite easy- people trying to do harm are EXTREMELY lazy- for example, in this instance they haven't done anything themselves and are going about it like they are giving us an assignment.
Also- In this case, at least- if they are aware of the /y switch they should also be aware of the /S switch so they could easily do it themselves.
Also- It's simply not possible to use a Innocent until proven guilty method, since by the time they would have proven their Guilt, the damage is done.
Even in the case were the poster is legitimately wanting information- such as in this case, deleting a tree of files - any information we provide can easily be translated into a malicious script.
Additionally This particular poster looks like... well, I forget his name, but he's been creating new accounts and asking similar questions as that for ages.