LFS2, you raise valid issues of how Koreans, colonized since 1910, dealt  with the reality  of their  brutal occupation  by Japan; some, as you describe, chose or were forced to be members of the Japanese military. 
 In a powerful book on WWII, "War Without Mercy" author John Dower discusses the Japanese use of Korean soldiers  to guard POWs and, as others, mentions their excessive cruelty. However, he adds CONTEXT: "Between 1939 and 1945, close to 670,000 Koreans were brought to Japan for fixed terms of work, mostly in mines and heavy industry, and it has been estimated that 60,000 or more of them died under  the harsh conditions of their work places.  Over 10,000 others were probably killed in the atomic bombing of  Hiroshima and Nagasaki." (p. 47)

Now, LFS2, a question- were you suggesting that  postwar South Korea's leaders were more likely to have been Korean "Quislings?" Sounds like the old "East Germany- West Germany" argument.