I Don't mind   is used a lot in different contexts ,       It can be  meant as  not taking offence at what someone said 
EG  ...  " Please don't be offended but your ass looks fat in that dress .."  Reply  " I dont mind at all "   THWACK ... 
  But as in this case   "  I dont mind  "   means  that I don't have an opinion either way and will go with the majority rule ...
It can also be used , if you borrow something,    "  Can i borrow your mirror?  "     " I dont mind"  =  yes if you want,  
Hope that clarifies it ...  there's probably lots more examples
"I don't mind" , is a polite way of saying  " I don't care"  which would be considered rude.