Muscatine

According to Iowa Code: 321.256  Obedience to official traffic-control devices:
"No driver of a vehicle shall disobey the instructions of any official traffic-control device placed in accordance with the provisions of this chapter, unless at the time otherwise directed by a peace officer subject to the exceptions granted the driver of an authorized emergency vehicle. "

The traffic control device is the stop sign. You all know what to do at a stop sign, right? When you wave someone through your are asking that person to disobey the stop sign. Yes, they stopped. But now your asking them to the break this law:

321.319  Entering intersections from different highways.
When two vehicles enter an intersection from different highways or public streets at approximately the same time, the driver of the vehicle on the left shall yield the right of way to the vehicle on the right.

Now Big Bother, lets check the Iowa code about rendering aid:

321.263  Information and aid--leaving scene of accident.

1.  The driver of a vehicle involved in an accident resulting in injury to or death of a person or damage to a vehicle which is driven or attended by a person shall give the driver's name, address, and the registration number of the vehicle the driver is driving and shall upon request and if available exhibit the driver's driver's license to the person struck, the driver or occupant of, or the person attending the vehicle involved in the accident and shall render to a person injured in the accident reasonable assistance, including the transporting or arranging for the transporting of the person for medical treatment if it is apparent that medical treatment is necessary or if transportation for medical treatment is requested by the injured person.

2.  If the accident causes the death of a person, all surviving drivers shall remain at the scene of the accident except to seek necessary aid or to report the accident to law enforcement authorities. Before leaving the scene of the fatal accident, each surviving driver shall leave the surviving driver's driver's license, automobile registration receipt, or other identification data at the scene of the accident. After leaving the scene of the accident, a surviving driver shall promptly report the accident to law enforcement authorities, and shall immediately return to the scene of the accident or inform the law enforcement authorities where the surviving driver can be located.

Doesn't say anything about directing traffic.

You wavers may be liable for damages if an accident occurs...

http://blog.oregonlive.com/commuting/2009/07/friendly_wavethrough_road_to_t.html

Anytime you direct traffic, you are impersonating an officer of the law, even at an accident scene. I've seen some idiots try to direct traffic at a mere fender bender. They almost caused more accidents. Leave the traffic directing to the trained professionals. You can put out road flares or those orange triangles to alert oncoming traffic, but other that that, render aid to the injured. Of course, if you're not properly trained in first aid or CPR, please leave me be. I don't need addicitional injuries. And yes, you are liable if you inflict more harm in your valiant effort to render aid.

Some wavers are malicious:

http://blog.oregonlive.com/commuting/2009/07/readers_hate_the_wavethrough.html

Another reason I'm ignoring the "Wave-Through," thank you very much. I think I can drive safely on my own. I don't need your help. Please obey the signs and get going.

Wow....this whole premise is quite a stretch.  Sounds to me like one of those "pet peeve" things taken to an extreme, like a first grader who can't get his way and runs kicking and screaming around the playground until somebody agrees with him.  Funny how what some see as a mere coutesy can be seen as "malicious" by others.