That’s an amusing explanation. Why amusing? Because you can use every point to argue that Rubio is the best choice.
Process:
Purists: Rubio is pro-amnesty!
Realists: Yes but on every other issue he votes with us and he says he will enforce current laws.
Purists: But he voted for amnesty on Gang of 8!
Realists: He beats Clinton and Sanders in head to heads, has a strong Latino following, and can deliver Florida. He has all the demographic boxes checked.
Purists: But he BETRAYED us on amnesty.
Realists: Pure conservatives can’t win elections. Stop being a one issue voter. This election is about taking our country back and to do that we have to WIN.
If it were the only formula that mattered, perhaps. But it's not.