って言うんだ is the casual 'that's called X / you call that X.' 先入観 '(a) preconception / prejudice / fixed idea' is a formal compound 先入 'enter first' + 観 'view.' 体験したこと無い 'never experienced it' uses the こと experience-aspect pattern with dropped が. ~のに marks the contrastive 'even though.' 決め付ける 'to pigeonhole / arbitrarily decide' is a compound of 決める + 付ける, with a judgmental tone. The trailing っ at the end marks an emphatic glottal stop.