Israel attacked first, and you don't get to steal someone's stuff even if they did attack you.

“I do not think Nasser wanted war. The two divisions he sent to The Sinai would not have been sufficient to launch an offensive war. He knew it and we knew it.” — Yitzhak Rabin, fifth Prime Minister of Israel

“In June 1967, we again had a choice. The Egyptian Army concentrations in the Sinai approaches do not prove that Nasser was really about to attack us. We must be honest with ourselves. We decided to attack him.” — Menachem Begin, sixth Prime Minister of Israel

The "buffer" made Israel less safe, not more.