The Collaborative International Dictionary of English v.0.48:

Wrongheaded \Wrong"head`ed\, a.
   Wrong in opinion or principle; having a perverse
   understanding; perverse. -- Wrong"head`ed*ly, adv. --
   Wrong"head`ed*ness, n. --Macaulay.
   [1913 Webster]

WordNet (r) 3.0 (2006):

wrongheaded
    adj 1: obstinately perverse in judgment or opinion; "a
           wrongheaded policy"

Moby Thesaurus II by Grady Ward, 1.0:

48 Moby Thesaurus words for "wrongheaded":
   Boeotian, asinine, balky, beef-brained, beef-witted, blockish,
   bovine, bullheaded, cantankerous, chumpish, cloddish, contrary,
   cowish, crass, cross-grained, dense, difficult, doltish, dullard,
   dumb, duncical, duncish, fat, froward, gross, headstrong,
   ineducable, irascible, klutzy, lumpish, mulish, oafish, opaque,
   ornery, perverse, pigheaded, restive, self-willed, sottish,
   stiff-necked, stubborn, stuffy, stupid, sulky, sullen, thick,
   unteachable, wayward