I normally do not weigh in on matters such as this, but in  my personal opinion I see nothing intrinsically wrong with a US Marshal or any other law enforcement agent  as a character...they are ultimately people too.  Though in Slice of Life Rp’s  it is pertinent  to  note that ninety-nine percent of the time a character will not be doing law enforcement duties they’d instead be interacting with the player base as a large. Even Superman is Clark Kent once in a while and so on.