This is a charade - multiple parts are combined in sequence to build the answer. Look for different sections that need to be joined together.
Break this into three parts: 'This setter's' gives you a contraction for 'I am', then take alternate letters from 'upset' (the regular/even-positioned letters), and finally reverse the abbreviation for 'editor' since it's described as 'contrary'.
Answer: IMPEDE | I'M (this setter's = I am) + P-E (regular letters from u-P-s-E-t) + DE (contrary/reversed ED for editor) = IM + PE + DE