I agree with two basic premises: first, MMA and boxing are related, but ultimately very different sports. Two, unless competing under strict boxing guidelines, the MMA fighter should generally be the favorite in a fight with a boxer.
What I don't agree with is the idea that the sports are so different that comparison becomes meaningless. The boxing lobby, on the other hand, does and issues this faulty logic to diffuse criticism of their very beloved sport:
The fact is that most boxers or boxing enthusiasts believe a boxer should be able to defeat any sort of combat athlete. I've been reading in Sam Sheridan's book a story of a boxing trainer who believed he'd figured out the weakness of Thai boxing and thought his boxers would be able to dispatch with the best Siam has to offer.
I could go into a lengthy diatribe of why that's preposterous, but instead I'll just post this video: