Arming Hamas could have been avoided.

Israel decided to weaken the PLO to undercut any movement towards a settlement that would include an independent state. Israel provided Hamas free passage as well as allowed money to maintain it.

There was one, and only one, election held that placed Gaza under Hamas control. Hamas did not allow any further elections. To blame all Palestinians and destroy what little they have is collective punishment. Geneva Conventions view this as illegal.

Israel created Hamas and, apparently, arms them as well.