I don’t think anyone would pretend they did not know of the destruction. I don’t think anyone is surprised that conducting military activities within a densely populated urban area would result in significant civilian casualties. That’s why what Hamas has done - embedded all of their military forces within a civilian population - constitutes a war crime. Because when that belligerent force attacks another party (here, Israel), then the resulting military response will cause significant civilian casualties regardless of whatever efforts the other party makes to avoid those casualties.
If Hamas has located its military forces, equipment, and materiel in Rafah, then there is no way that Israel can attack them without significant loss of civilian life. Which, again, is why it is a war crime for Hamas to have done that.
Note, however, that because Hamas has embedded all of its belligerent assets within a civilian population, an attack by Israel against those forces would not necessarily constitute a violation of international law or any treaties. Again, embedding forces among civilians doesn’t mean that the belligerent force is somehow on “home base,” and immune from attack - it merely imposes obligations on the attacking force in how they conduct their attacks. Which is why the UK isn’t suspending their arms exports licenses now, or categorically saying that they will if the Rafah offensive goes ahead.