Last time I looked, every single action revolver could be cocked by the thumb of the same hand holding the revolver while every pistol I've seen requires two hands to rack the slide. Perhaps you are aware of an exception?
Everyone who's survived a deadly confrontation where they racked the slide before taking action against the target will tell you they were never too busy to rack the slide. Those who didn't have time to rack the slide won't say anything, they're too busy being dead.
Using two hands to rack the slide is perfectly fine as long as you can always guarantee
You won't be carrying anything in your other hand
You won't be holding on to your child's hand, or your wife's, or your husband's, or your lover's.
You won't be hanging on to the leash of a pet that's frightened and pulling away
You won't be hanging on to the arm of someone fighting or assaulting you
You won't be injured in your other hand so as to make it useless
You won't be hanging on to a pole, a ledge, a doorway, or anything else to keep from being dragged
Your S.O. won't have a death grip on your off hand out of terror
... that's a few too many "won't be" assumptions for me to want to risk, but everyone has a right to determine their own risk level.
Saying, "I'll load the pistol once it gets dangerous" is like saying "I'll put on my seat belt once traffic gets dangerous." Seat belts and defensive firearms are there to meet dangers that you didn't anticipate. If you anticipated possible danger when driving you'd have put your seat belt on before you left your driveway.