Legalizing wagering on which team wins or loses a particular game,
while banning all bets on immaterial outcomes like point spreads, would
destroy the market for illegal bookmakers and make sporting events less
corruptible by gamblers.
Point shaving may be widespread enough to have occurred in around 1 percent of N.C.A.A. basketball games.
Here is the full argument, and thanks to Chris F. Masse for the pointer; Chris also points me to this new and possibly very important study (a senior thesis by Jonathan Gibbs, at times the link isn’t working) of point shaving in the NBA.