Protestants weren't the only sources of that representation; peasants regularly became angry at monks, because they imagined their life as being luxurious and idle - of course, they were right compared to their life.
Moreover, it wasn't done always to make the other side look bad; in Rabelais' epics, the lecherous war-loving wine-drinking monk is one of the most endearing characters. In Friar Tuck's case, I think it's part of the second tradition.