Then were do you draw the line? Shall we just equip the crew with Starfleet-issue wands? Remember that Khan was the product of centuries-old medicine and science. Why can his blood cure people that 300 more years of medical advances cannot?
I would draw the line at people making mountains out of molehills, but the amazing, and wholly practical, Genesis Device has already ignored that line.
It's funny because as a friend and I were nitpicking afterward, he asks me, "So now they can just cure anybody of death that they want to?" And he's just like a moderate Star Trek fan.
It was me. ME! The hardcore Trek nerd who had to explain how many times before people had been resurrected in the past and I said, "Well, they had the whole Genesis device thing and we all accepted that."
And I laughed at his response which was, "Well, I never accepted it." It's true. A lot of that stuff is silly. We kinda came to an agreement that you just have to let a lot of it slide and move on, but that doesn't mean that you can't at least point it out when it happens as being somewhat odd. The Genesis device and Spock's Katra thing is exceptionally ridiculous. Magic blood has nothing on it.
But it does establish a stronger precedence for what was one of Trek's particular dramatic weaknesses: main characters just don't really seem to die and stay dead.