Your facts are not correct. Israel immediately expressed regret and in fact this came from the Prime Minister himself. Don't believe me? Search "netanyahu regret flotilla" on Google, and go to a link on BBC News. BBC is well known to be hostile to Israel. This was even reported in aljazeera,net. So no, Israel clearly expressed regret for loss of life (unlike Erdogan The Butcher who never expressed regret at the Turk massacres against our people). Israel simply refuses to apologize for defending themselves. I wouldn't apologize for such situation either. USA, Britain, Russia, China, any arab coutry would not apologize for this either. Self defense is always justice.
U.S. to defend Syrian rebels with airpower, including from Assad (Reuters)
from the article: Israel: We will not apologize to Turkey over Gaza flotilla deaths