I. How are we defining "successful"? I would say that if my kid is happy in whatever they're doing, they ARE successful.
II. I would rather my kid (or anyone) have the most opportunity for personal growth possible than to be subject to any arbitrary system. Who came up for the criteria of whether my kid could advance? Why should that entity have the power to decide how much knowledge a person has access to? This is assuming that not cheating would prevent the kid from further education altogether. Since the question implies that they would still have oportunities at other learning institutions, I say the kid should sink or swim on his own merit.
In other words, education is a right that should never be denied. But as long as there is general access to it, the individual educators have the right to set standards for whom is accepted to their institution.
Thanks, I like questions that make me think.