Aggression by NI is only justified if it feels its safety threatened (though definitions of 'threat' and 'safety' vary to some extent within the NI government). NI reacts swiftly, viciously, and finally in defense or retaliation. It will not attack civilian population, but it will excise any active military threat it can find, no matter where it hides. The more hawkish within the government feel that if a group appears to pose a threat, it is by definition not civilian. Hawks are currently well balanced within the government, however.
New Israel sometimes acts pre-emptively, but only after long and careful internal deliberation and assessment of the cost in lives and resources, and the ripples it will cause in its foreign relations (usually not visible to the outside). _Something_ will have been learned from the political history of Old Israel on Earth, although sometimes internal pressures and politics may force it to act and live with the external consequences.
Planets/bases are heavily (to the point of paranoia) defended. New Israel itself (defended by bases and the bulk of the NI fleet at most times) would require a substantial part of a major power's fleet to take out. It is theorized that the entire IF fleet en masse could do it, but at a steep price.