Here's what rhymes with unprincipled.

Consider these alternatives

amoral / moral shortsighted / decided hypocritical / critical opportunistic / characteristic unfeeling / feeling perfidious / tedious uncouth / truth devious / previous imprudent / student underhanded / advantage undignified / side immoral / moral irresponsible / responsible impudent / student conniving / driving unpatriotic / logic brazenly / masonry unseemly / extremely