A problem with the delete is that it can totally mess up the context of a thread and give anyone contributing to the thread editorial control of posts after his/hers.
There was a person on another forum site who routinely edited his posts, not for typos etc...but effectively changed his posts meaning and context. Given he was rather contentious, he'd do this if the collective opinion went against him. At least, he didn't have plausible deniability with that big ol "edited by____ on Mar 9, 1998"
As Ewok noted, you can effectively do it by editing away the text...but the "edited by" remains
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"Quis custodiet ipsos custodes" RKBA!