It may be a useful survival trait in some sense, but it's not useful in others. Often I run into situations where people lose their heads over something that is not a real issue.

"EEWW!" "Oh, the bucket is full of maggots? OK, let's go dump it in the woods." "Oh, I couldn't possibly do that! EEWW!"

Or people will freak out over some feces or urine, and stand around discussing how disgusting it is rather than just cleaning it up.

I imagine doctors have similar opinions about normal people and blood (not a reflex I've had much luck with controlling consciously).

More importantly, this is a kind of mindfulness meditation, which generalizes - if you can step back from maggots or feces and ask yourself 'is this really something to be perturbed by?', then surely you can do the same for many other issues. (I have read that sometimes Buddhists or Hindus would meditate in front of rotting corpses, but that's probably taking it a bit too far.)