Robin was persecuted by the world and the only person willing to stand up for her and make her admit she wants to live is a charcter with the simplistic ability to see right and wrong reagardless of who makes the rules.
Yes there is some romanticism in that which may appeal to many, but it's BAD WRITING. It a day-dreamer's phoney solution to a convoluted scenario.
Do you think that
There is no way a character like Robin would believe for a moment that Luffy would understand her problems, so the show needs to do something theatrical like shoot down the government flag.
A spectacular moment to be sure, but way too easy. Now all of a sudden her thinking reverses 360 degrees andshe believes that he is the right savior for her? are you kidding? How does such an action convey that they are suddenly trustworty. An intelligent character would look at the action and merely see recklessness not empathy, so the show spells it out for us, by telling us that is is an emotional gesture, and asking us to accept that Robin feels that way.
Again, the one who REALLY understands her best is Franky.