Reasonable . . . hrm. Hard to say. The surface area of duties and rights associated with an airline ticket in particular and airline travel in general are so vast that some level of clickwrap is unavoidable, not to mention the various laws that cover the industry.

Comparatively, the duties and rights regarding a physical good like a sandwich are fairly simple -- it behaves like most simple physical goods. You buy it, then you can do what you want with it. Airline tickets are unlike this in a variety of ways. Hidden city routing being prohibited would not, I feel, be qualitatively different than many of these other restrictions.