Thing is ... the cops were just following protocol, which means someone should start thinking about protocol.  82-year-old Martha Menefield opened the door of her Valley, Alabama home and saw 2 cops with an arrest warrant.

Martha was delinquent in paying her $77.80 trash bill and that was enough to hook her up and take her to the station.

One cop tried to comfort her, saying, "Don't cry, Ms. Martha."

Body cam vid shows one of the officers laughing at one point ... hopefully the laugh was the absurdity of arresting someone because they can't afford the basics of life.

She says she thought she had paid the bill, but the cops said they had to follow protocol, which was to handcuff her and take her to the police station.