There's a significant cost to process the oils/lipids, get rid of the solids, etc, right? Many communities have well-funded public awareness programs to discourage people from putting oils, fats, and lard down the drain. And people who put hydrocarbons into the sewer should be prosecuted.
I wouldn't balk at putting a teaspoon of oil into a trap to keep the water from evaporating. But I do wonder why people dump a pound of meat trimmings down the drain, running the garbage disposal for 2 minutes to wash it down. The trash can is right there, it takes less time just to throw it in, and you're not putting a burden on the city water treatment system and wasting 5 gallons of water (praying it gets to the street and doesn't clog up your sewer pipe.) Are people that worried about how their trash might smell?