A question regarding do-overs: (Not meant to be inflammatory)

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Now, I know that Fla. and Mich. are a hot topic. But I have two questions regarding whether a do-over is acceptable, and I think they're fair ones:

1.) In those primaries, many already cast their votes once. Others crossed the aisle and voted for the Repulicans, because they knew that their vote would have no meaning.

So, wouldn't a do over essentially allow them a "second vote"? The ability to vote in both the Republican AND Democratic primaries? Or two votes within the primary? That seems to violate the "One person, one vote" rule.

2.) If we allow it this time, then what's to stop other states from fucking up the system in the future? What if they say "Well, you let Fla. and Mich. have do overs after you censured them? They'll have to give us the same treatment!"

Again, not to be inflammatory, but these seem to be important questions as to the reliability to the primaries. How can we allow the denizens of these states to essentially have two votes?