Human ethicists have long struggled to come up with a coherent ethical theory that determines whether tickling humans is morally acceptable.

I'd say it is iff the humans consent to be ticked. (But they needn't consent unconditionally; they may e.g. consent on condition that the martians pay them money.)

(This is what sprang to my mind straight after reading the quoted paragraph, before I realized what this was an allegory for, but I still stand by it.)