na-adjective, noun
unprincipled; inconstant; unscrupulous
Describes a person or behavior lacking firm principles, easily changing opinions or acting without moral consistency.
彼は無節操な態度で、誰にでもいい顔をする。
He has an unprincipled attitude and tries to please everyone.
無節操に意見を変える人は信用
You can't trust someone who changes their opinion without principle.
一貫性 refers to 'consistency' in a neutral sense, while 無節操 carries a negative moral judgment about lacking principles.
Compound of 無 (mu, 'without') and 節操 (sessō, 'principles, constancy'). The reading むせっそう reflects a common gemination of the initial consonant in the second element.