I don't think it is "criminal" in terms of you going to serve time (necessarily), but it is still criminal in the sense that it is a breach of your agreed upon contract of carriage between you and the airline. Isn't that fraud? As AC*SE pointed out, the airline can take action by rescinding your FF account and maybe even blacklisting you.

BTW, I'm not trying to defend the airlines here. I think the prices they charge are indeed criminal.

FewMiles..