Conspiracy Theories -- explanations for events that invoke witting, nefarious designs and elaborate plots directed toward the exact ends achieved when more parsimonious explanations fit the available evidence -- I would argue, are never benign. In the case of claims of Satanic Ritual Abuse, the immediate consequences of a belief in this conspiracy theory are quite clear: specific individuals are accused of crimes they never committed, families are destroyed, personal liberties are threatened or stolen.
Alien abduction claims may be less obvious in their harmful consequences. But, as a belief in these ET incursions in human affairs is also dependent on recovered "memories" (or, rather, false memory creation), arguments in defense of Abductee recall of "repressed" memory lend support (if taken seriously) to false memories of the directly accusatory kind. And both camps are obligated to vehemently reject the science that explores mechanisms and processes of false memory creation, often demonizing the scientists in the field.
Even if the Conspiracy Theorist were to be found to be living his/her optimally fulfilling life deluded by stories of massive underground treachery (and I don't think anybody could reasonably argue in defense of this proposition), this would not excuse the inevitable targetting of individuals felt to belong to the conspiracy's inhuman machine.
Conspiracy Theories always suggest an enemy to be defeated, an evil other whose destruction becomes the highest calling to the true believer.
Perhaps it was all fun and games when conspiracy-shouting radio host Alex Jones lied to his audience (knowingly) to sell a new bit of "9/11 Truth" lore. But one would have hoped the amusement would have died back in 2002 when a crazed Jones fan attempted to enter Bohemian Grove "hoping for a shootout". Jones, of course, is famous for loudly denouncing the old rich man's retreat as a center for elitist conspiracies with a Luciferian bent.
Recently, Jones protested that Glenn Beck has been stealing his ideas. That Beck's research could have led him to the same place as Jones, you see, is impossible, for these are not positions based on facts.
Not surprisingly, a crazed fan honored Beck in a shoot-out with police when he was intercepted on his way to massacre "progressives".
Given the rhetoric of characters like Beck and Jones, it's somewhat surprising that these things don't happen more often... but they'll surely happen again.