Once again, you're misrepresenting the historical record. The pilots were certainly shocked and repeatedly said that they hoped nuclear weapons would never be used again. However, they did not express regret for what they did:

"I honestly believe the use of the atomic bomb saved lives in the long run. There were a lot of lives saved. Most of the lives saved were Japanese."

-Capt. Van Kirk (navigator)

"it was just a job of work. I helped make the world a safer place. Nobody has dared launch an atomic bomb since then. That is how I want to be remembered. The man who helped to do that."

-Capt. Lewis

"No, I had no problem with it. I knew we did the right thing because when I knew we'd be doing that I thought, yes, we're going to kill a lot of people, but by God we're going to save a lot of lives. We won't have to invade."

-Col. Paul Tibbets (commander and pilot)