Have you ever worked at a job in the public domain? I mean, in a resturant, or at a Walmart, Home Depot or some place like that? I have, I spent my high school and college years working with the public.
Most of the public is like you or I. Polite, earnest and know what we want. There are those members of society, those who have never worked, who see this as an opportunity to abuse someone who can do little, if anything to defend themselves.
I've seen people walk into an Olive Garden, angry about something, and take it out on the waitress. She had nothing to do with what happened, she trying to make tips to go along with her $3/hr job; so she can feed herself and perhaps her family. She gets to take the abuse, do her best to appease the abuser, and then still hope her abuser see's fit to leave a small tip.
I've seen people chew a Home Depot worker out, because the paint they bought wasn't sticking to the cement like they had thought it would. The Home Depot worker repeated that he didn't sell them the paint, but would gladly refund their money - yet this wasn't enough.
In my examples, profanity was not offered - just abuse. When you work in a public setting, you are told that you may have to deal with unhappy customers, but you do not need to take their abuse.
So, lets look at the IRS, DMV, VA, Post Office, DPSS, shall we? These people are constantly berated. The best that they can hope for, is to do their job and not be abused. Think about the guy in the Post Office, mailing packages. What do you suppose his 'Best' day is like? The DPSS deals with rude, in some cases drug-addicted, unemployed/unemployable people who may or may not have any inclination to work. Yet, these workers are expected to come dressed professionally, be polite, and keep records on every visitor - many of whom have not had a bath in days. The public they serve may be as rude, as obnoxious and as demeaning as they want, they can demand anything and throw tantrums. They can, and some do. What response can these people offer? Simply put, their options are limited - but making the rude one's wait is about it. My wife worked for our state DPSS - it was far from the panacea you describe.
Visit your DMV and sit and watch them work; it's unending assembly line of thankless tasks. They have job security, but their work life is drudgery. If someone fails a test, who's blamed? The pay and benefits vary state to state, I can't talk about your state, but here in Utah the starting pay is pretty low. Let's simply say that it's not a 'fun envirnoment'. The idea that because you work for the gov't; you are supposed to take abuse, or profanity carries no weight whatsoever. Again, you wouldn't dream of demanding that people at Walmart, K-mart, Target, Sears or any other commercial venture sit there and take verbal abuse. We are perfectly able to convey thoughts, concepts and points of view without once uttering a single profanity. No one, absolutely no one should be in a position to be the object of ridicule.