I confess that I haven't read through this whole thread, but am just jumping in now.
Is evil necessary in order to know good? No, but it sure gets us off our lazy behinds dosen't it?
Seriously, we exist within a realm (3D physicality) where polarity exists. It dosen't at higher dimensional levels. We come 'down' into polarity to experience It, to get our teeth kicked in by It, to be killed by It, to become strong and wise because of It. Then, of course, we
ascend above It and exist at a slightly higher vibrating dimension where polarity dosen't exist. Cycles of learning.....