I know and understand that there is no such thing as a delete Button in issues, repositories, etc. to make sure to have everyone understand that deleting such an element is a forcefull task which shall not be done on a regular basis and therefore use the Commandline Client instead.
But there are situations where this is difficult: Taking this instance of Phabricator for example: Most users will not have shell access to this - so all "we" have is this web view. When we select a wrong image or other files and drag it over into a mockup, issue, etc., it IS in there and without the ability to delete it, it will stay in there forever.
There is a workarround for some of these cases: One can set the "Visible to" permission to only the own user, so someone other than the site admin cannot see it any longer. But if this happens for a reply on a maniphest task for example, you only could restrict the whole issue, not single elements in that. And even this will only work, if you have proper permission on this issue.

I see strong problems in this: When I imagine I grab a copy of an important "Do not distribute" company draft instead of a screenshot or such, I will have big trouble because of using Phabricator and no really good way of solving this. The only way I can imagine will be to have an Administrator remove it. But this will take minutes to hours during it is exposed to everyone.

I would be very happy with the ability to remove elements in the Web-GUI, too, or the ability to restrict permission to entities like single replies to Maniphest tasks , too.