When does "self-defense" become naked aggression?

Israel is begging that question in three places:

Gaza, Iran, and possibly Lebanon 

Take Iran.

If Israel took the position:

"We are going to unilaterally destroy any capability for Iran to build either nuclear weapons or ballistic missiles", 

that could be construed as taking acts necessary for Israel's defense, 

namely, eliminating threats.

But Israel has gone way beyond that.

It has not merely attacked facilities that produce weapons, it has assassinated numerous Iranian leaders.

I will state this unequivocally:

Israel had and has NO valid justification for controlling who rules Iran.

Disarming Iran is one thing.

Determining who is allowed to rule Iran is an entirely different thing.

How many Iranian leaders must be killed to satisfy Israel?

Killing soldiers and war-fighters is one thing.

Killing leaders is a totally different thing.