Pardon my naivety, but why would a third party want to set bots onto Facebook ads? I guess one could hope to exhaust a competitor's marketing budget, but surely

Pardon my naivety, but why would a third party want to set bots onto Facebook ads? I guess one could hope to exhaust a competitor's marketing budget, but surely this isn't an established tactic. Even more Machiavellian would be Google doing it to discredit Facebook's entry into the advertising business. I doubt this because they've got too much to lose - if they were discovered, it would seriously hurt their "don't be evil" reputation, which is worth billions to them. And just imagine the anti-trust suit... Although Facebook stands to gain the most from this, my argument about reputation damage applies there too. So who is paying for the bots?