the death of shinn family causes him to be sort of loner...
it causes shinn to think/act differently from those with family...family love o.O

he was just a little young 14 years old boy...who have mayu,his father and his mother and their love
living in a world that was filled with happiness
but however...its too sudden that all your family members around you have died in an INSTANT...
its too much for shiinn to handle...causes him to see life negatively...
causing him to see things in hatred instead of understanding/concern/love

shinn actually love orb and have faith in orb when his 14 and orb idealism
shinn parents also believe that they would not got into war as long they r in orb
the hatred against orb was due to his faith and love for orb...
in one episode i do remembing athrun said that something like
shinn blaming on orb aint it because of the faith shinn put in orb

the only way to prevent stellar from dying is to return stellar back to EAF...
and when you saw your love ones dying...you would not consider what would she do in the future...
the only thing you think off is whether she could stay alive for now

the only thing shinn tries to protect is stellar...
stellar causes a big change in shinn for the first time that shinn actually tried to protect someone...
also its true that kira killedied to fire and killed three towns o stellar only because stellar trf civilians and who can say its wrong

but its only natural that you blame the one who causes her death directly(your love ones) somemore
when your love ones death, i dont believe you would be bother to consider who kill her indirectly
but you would hate and wants to kill the one who causes her/his death directly thus its kira