Sasuke is one of the most selfless people.
When has Sasuke ever done anything out of selfishness?
His entire life has been about avenging the slaughter of his Mother, his Father, and his clan. Is that selfish? To put his own life at horrible risk for people who aren't even alive anymore, just so the pain inside his chest has meaning? To make sure, that his Brother's horrendous suffering doesn't come to naught.
To loose himself in hatred, abandon every decent thing in his life, for a cause that was lost long ago.
An eye for an eye. Has anyone ever gained anything from that? They have only lost.