People can have their opinions about everything in the world, but people's opinions end where the tip of my nose begins. Your opinions of others can only go so far as to where their own shoreline is. The world is for your taking, but other people are not. One is only allowed to have an opinion of me, if that person is done educating him/herself on everything about me. Before people educate themselves on everything about you, they're not allowed to open their venomous mouthes and have an opinion about you.
Remaining for a moment with the question of legality and illegality: United Nations Security Council Resolution 1368, unanimously passed, explicitly recognized the right of the United States to self-defense and further called upon all member states 'to bring to justice the perpetrators, organizers and sponsors of the terrorist attacks. It added that 'those responsible for aiding, supporting or harboring the perpetrators, organizers and sponsors of those acts will be held accountable.' In a speech the following month, the United Nations Secretary General Kofi Annan publicly acknowledged the right of self-defense as a legitimate basis for military action. The SEAL unit dispatched by President Obama to Abbottabad was large enough to allow for the contingency of bin-Laden's capture and detention. The naïve statement that he was 'unarmed' when shot is only loosely compatible with the fact that he was housed in a military garrison town, had a loaded automatic weapon in the room with him, could well have been wearing a suicide vest, had stated repeatedly that he would never be taken alive, was the commander of one of the most violent organizations in history, and had declared himself at war with the United States. It perhaps says something that not even the most casuistic apologist for al-Qaeda has ever even attempted to justify any of its 'operations' in terms that could be covered by any known law, with the possible exception of some sanguinary verses of the Koran.