The 'activists' killed were killed for a very good and legitimate reason. They attacked IDF soldiers sent onto the ship who legitimately were there to prevent the ship's entry into Gaza, then tried to take the injured soldiers as hostages. The response by the IDF was forced upon it by the activists actions.
20 killed, dozens wounded in bombings in Sanaa, Yemen (Reuters)
from the article: Turkey may expel Israeli ambassador in wake of Gaza flotilla report