Even though it may be courteous it could be against the law.

According to Arkansas Law: It is illegal to operate a vessel at a greater than "no wake speed" within 100 ft of a designated rec area, dock, pier, raft, float, anchored vessel, dam, intake structure, or other obstruction.
"No wake speed" is defined as not producing a wake or 5mph or less.

I am not one to want to argue with the law and try and convince them a boat wasn't anchored, and who knows what "other obstruction" is defined as, so I prefer the idle speed when passing other boaters.