Synonyms for Wrongheaded:

adj.

contrary (adjective)
perverse, obstinate.
dogmatic (adjective)
prejudiced.
obstinate (adjective)
perverse.

n.

stubborn (noun)
biased, prejudiced, perverse, narrow, obstinate.
wrongheaded (noun)
wrong.

Other synonyms:

Other relevant words:
biased, prejudiced, perverse, narrow, obstinate.