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.
Getting a bit philosophical there, with the morality aspects. But I digress. Avenging for the sake of family and clan could of been seen as retribution, or noble. But Sasuke no longer sees Justice. Konoha's destruction will only serve to make himself feel better (and cheers from Konoha's enemies). So, I strongly disagree with you, Sasuke is
not 'selfless.' Think about it from this point of view. A selfless person would not seek power for simply revenge, or try to kill their own best friend (which he DIDN'T WANT to die), or have so little compassion for others' emotional vulnerabilities. Still not convinced?
Definition of "selfless" here are the following
Google: concerned MORE with the needs and wishes of OTHERS THAN ONES OWN.
Wiki-answers states of being "compassionate" and "humble" for the sake of "others."
dictionary.com: "having little or no concern for oneself, especially with regard to fame, position, money, etc.; unselfish."
oxford dictionaries: same as Google's definition.
Cambridge dictionary: "Someone who is selfless only thinks of other people's advantage"
Wiki: "the act of sacrificing ones own interest for the greater good"
Getting the curse mark, who did that benefit? Leaving the village, who's desire was met? Gaining power for revenge, where was the greater good in that? Finally, when has Sasuke ever shown real humility or compassion to others? Just compare the definition to Sasuke's actions, do they match?
I'm not a Sasuke hater. But perhaps its a good time to rethink on the ideas of revenge, retribution, noble, and justice.