Who defines "reasonable"?

When you get delayed on a flight due to a maintenance issue, are you equipped to determine if that delay was reasonable? Most likely not, although many mechanically inclined people may be in a position to make that call. Those same people may not be in a position to arbiter the reasonableness of Google's ToS (side-stepping the whole obfuscation of details that was previously covered).

When society gets reasonably complex, we out-source those decisions. In the example of the aircraft, we have a regulatory body who makes the rules about what is reasonable. It wasn't always like that, of course, but the need grew out of the growing complexity and risk profile. So to your question and an earlier point, there may be room for regulatory bodies as an alternative for "how else can it work?".