I'm coming a little late to this thread, so I apologize if this has already been said.
I think what is being argued by
@Saelorn is not that the freedom to do whatever makes whatever choices "in character," but rather that the freedom to do whatever allows me the freedom to come up with whatever personality(character) I want for my PCs.
If the game incentivizes only 3 of the 2 billion(arbitrarily large number to show that the number is large) ways to play a character, then the player has essentially 3 choices. 1) pick one of the few character personalities that the game rewards so as to be able to get the incentives and stay in character. 2) pick whatever personality I like and miss out on the incentives, gimping myself in the process. 3) pick whatever personality I like and play out of character in order to get the incentives. None of those are attractive options.
In my opinion, a game should take one of two paths when it comes to this sort of thing. The first path is to incentivize playing the character you come up with. This enables the player to come up with any personality type with quirks and such, inform the DM about it, and then use the system to reward the player for playing in character. The second path is not to have incentives at all, and let the players come up with and play their characters' personalities themselves.