I'm not sure the goal posts have moved, it's more the nature of this war. A lot of the time you see two armies going at each other. In this case, the Hamas strategy is to use the civilian population as cover.
Article 52 of the Geneva convention says, "Civilian objects shall not be the object of attack or of reprisals. Civilian objects are all objects which are not military objectives as defined in paragraph 2. ..... military objectives are limited to those objects which by their nature, location, purpose or use make an effective contribution to military action and whose total or partial destruction, capture or neutralization, in the circumstances ruling at the time, offers a definite military advantage"
Article 8 of the ICC clarifies this, in relation to war crimes, that, "(ix) Intentionally directing attacks against buildings dedicated to religion, education, art, science or charitable purposes, historic monuments, hospitals and places where the sick and wounded are collected, provided they are not military objectives".