"While Israel is perfectly within its rights to use assassination as a tool."

No state has that right. Except in time of war - and that is defined fairly closely, and the present situation with Israel is that it is not at war with Palestine - political assassination is classed as a terrorist activity. A state which indulges in it is acting criminally, the people involved in it can properly be tried for murder.

There are all kinds of justifications which can be made for organisational which see it as necessary to resort to terrorist methods. The Israeli government is one such organisation, and any arguments made in defence of its behaviour have to be grounded on acceptance of that fact.