Why most of employees think that the HR departments are not useful, and treat us as enemies ?

it is perception  but  not  correct HR  is department  which   bridges employee with  management   and vice  versa. they  are  custodian  of  the management to do  policy matter and  its implementation keeping  employee and  organization  in mind  . if  employee does  good  work   and  is professional   he/she  will not  fail and  will  be  liking  any organization  however  employee  who  does  not  perform or  have  discipline issue  than these set  of  employee  are  concern and  create   issue .