To avoid extending metaphor is important in any life or death situation. If one conceptual metaphor is allowed to act as precedent for choice of another, then, it is very easy to justify arbitrary actions of any kind at all:
There is no guarantee that the empathic integrity of the original choice of metaphor will be retained in those which rely on prior metaphors to make sense.
For example, to invent the idea of virtual community is to liken a simple group editing system to a physical place. Any such likenings have their own problems, see avoid the building metaphor. But these problems are very much compounded by extending the metaphor to other aspects of physical places:
Since such physical places have the risk of violent confrontation and exclusive property rights, those who accept the idea of this "virtual community" also can be made to accept the idea of "police" or "security guards" to "protect" people who are in fact in danger of nothing more than having their feelings hurt by harsh words. Sometimes to justify their power they try to have an impact on the real world, e.g. outing. This reprehensible behaviour willl seem to many to be justified since real "police" or "security guards" (not an untrained and unaccountable sysop power structure) are often "trusted" with when to perform otherwise reprehensible behaviours. When "virtual cops" perform such an act, e.g. outing, it would be unjustifiable to their peers if they were not being compared to physical behaviours by their real world analogs, e.g. beatings, torture, and etc. Thus, by comparison to "real thugs", the "virtual thugs" seem quite benign - maybe harmless - but in fact have justified quite dangerous behaviour by the building metaphor that eventually obscured the body reality of what they have done: involved a previously uninvolved body by force.
Sometimes extending metaphor is inevitable and appropriate, however, e.g. the overloading of the term "trolls" to identify heretics and outsiders in net forums, literally forces those so labelled to respond by building a mythological response with such elements as a world tree, Ragnarok, and so forth: this defensive use of metaphor to rally those oppressed by facists is not only excusable, but desirable, as long as it is avoided when it is not necessary. If there is no confusion with group entity then the risk of becoming overly identified with the mythological troll race is low.
Unfortunately, those who identify with police or paramilitary groups, and secretly wish to have powers to do unaccountable physical harm to others, seem to revel in the sysop role and actively invite confusion of their role with that of some real authority, often becoming enraged when there is no recognition of that claim by those who consider them usurpers.