We are thinking too much into this, as these are one-dimensional, fictional characters with a predetermined life of behaviors.
For the sake of the discussion however, Guld is nothing more than a scoundrel, a villain, whose evil behavior manifested itself at an early stage in his life when he assaulted Myung and Isamu for no justifiable reason at all (what other people do together is their own business). Later, he sabotaged the '19 project which almost ended in a tradgedy, then he "accidentally" thought something while flying the '21 that resulted in Isamu's crash, and then he tried to murder Isamu on Earth when it's obviously implied that he was supposed to merely stop Isamu from ruining the armstice ceremony.
Guld's personal sacrifice was the LEAST that he could do for the people whose trust that he had betrayed over the years.
In regards to the idea that Guld or anyone else could be a result of their upbringing and thus explaining anti-social behavior? BS. As long as Guld or anyone else has the capacity to discern right and wrong they can always make a choice; Guld chose to be a punk and deserved to die...