Some people really believe in mohammed.
Some people really believe in Joseph Smith.
Some people really believe in Mary Baker Eddy, Aimee Semple McPherson or Charles Taze Russell.
Some people really believe in L. Ron Hubbard and David Miscavige.
Some people really believe in Karl Marx.
Weird beliefs abound ... most of these believers didn't argue their way into their particular set of beliefs, and won't likely be argued out of them.
Love your enemies, pray for those who persecute you, do good to those who mistreat you.
May God grant them all the Grace of repentance and conversion.