It is part of the job....but that doesn't justify it nor mean it has to remain part of the job. Getting assaulted is part of what's inevitable in a copper, but that doesn't mean they can't minimise that risk, and it doesn't justify it or mean they have to tolerate it. It's not written into the job description - it's just something that, unfortunately, happens. A lot.
It's part of the job in the sense that, unfortunately, you inevitably have to deal with it. People say 'it's part of the job' without stopping to think what it means.
It's a bit like when people leave rubbish on the shelves at your local department store...yes, it's the job of the staff to clean that up, but only because people force them to deal with it! It's circular reasoning to condone abuse then say 'it's part of your job'