Why does my child fight the dentist?

Fear. Depending upon how old your child is, fear of the unknown ( or known! ) is usually the cause of the fighting.Most of the time a qualified pediatric dentist is able to work thru the fear to obtain the child's cooperation.
Fear of unknown. Your child's reaction is not uncommon, especially in kids who did not start seeing dentist 'till 2 or 3 (1st dental appt age 1). Perhaps child heard adults relating "horror stories." perhaps it's the smells, or the noise, or most probably just fear of the unknown. If your child is uncomfortable at your dentist's office, perhaps they should see a pediatric dental specialist.