I'm not claiming that it's a terrible crime. I just don't think that it's ethical. I sort of agree with the argument that "they deserve it"- they probably do deserve it, but I don't think that that justifies you doing it to them.

As to lisamcgu's advice- I would have one concern. Although the airlines do have more important things do worry about, they still seem to choose to sometimes busy themselves with petty things like this. I would consider it risky for two people put flights on the same account if one person couldn't have theoretically done all the flying. It would really make you trouble if an agent happens to look at you account. That's besides the point that Doppy raised- that the security people might react to it.