The most important reason to organize your government as a republic instead of a direct democracy is that voters can't always be trusted (a) to put the best int

The most important reason to organize your government as a republic instead of a direct democracy is that voters can't always be trusted (a) to put the best interests of the nation as a whole ahead of their own, or (b) to even know what their best interests are. "That was clearly a really self-destructive/evil/illegal/otherwise terrible idea once we spent more time thinking about it" is a perfectly fine justification in an ideal world. In reality, of course, it would probably be very difficult to explain satisfactorily to the electorate, especially the stereotypical Brexit/Trump "low-information" voter. One potential way to counteract this is through collusion by the MPs. If, for instance, all of Parliament were agreed that Article 50 was a terrible idea, but didn't want anyone to lose their seat over it, they could organize their votes such that they can all get out relatively unscathed. The ones from left-wing districts are probably okay either way, and then the conservatives just have to pick the handful that have the safest seats to be the nays that push it over the edge.