When something's forced on you, it's human nature to push back, isn't it?
Literal
Forced-[passive-られる] [conditional-と] resist-[contraction-ちゃう] [nominalizer-の] [subject-が] human [called-っていう] thing [isn't-it-なんじゃないか].
A casual philosophical observation. 押し付けられる (passive of 押し付ける 'to force on') + と (automatic conditional) sets up the cause. 反発しちゃう (contracted ~てしまう) signals the pushback is involuntary. 人間っていうもの ('the thing called a human') generalizes from individual to universal. なんじゃないか seeks agreement while softening the claim.