One of the hardest lessons to learn in life is that wishing doesn't make it so.
It's possible to view the history of science fiction as a long search for magic wands, for things that will fulfill the wish fulfillment fantasy. We've had potions and rays, ESP and PSI, interstellar empires, nuclear power, and radiation giving people mutant powers. Sometimes it's virtual reality, or cyberspace, the knurd imagination writ large. Sometimes it's something as simple as a new way to get laid (telepathically!).
So we come to parallel worlds and quantum indeterminacy, with the latter being shorthand for some method of wishing yourself into the parallel world that is to your liking. Some of this comes from the confusion that results when someone identifies personally with the word "observer" in the Copenhagen Interpretation. If you wish and wish with all your might, for Schrödinger's Cat to be alive when the box is opened, then, by golly, the Cat will live and come out to play with Tinkerbell.
But even if you take the "Many Worlds" interpretation, there are problems. Perhaps it excites you to imagine that there is a parallel world in which you are married to Angelina Jolie, but there are a number of problems with the very concept. First, even if there is a world in which someone who shared a timeline with you up until the lucky streak (for you; let's not consider what the situation would mean for Ms Jolie) that gave that result, that fellow isn't you. Not anymore. And this stricture applies even more forcefully to those worlds where "you" are of a different sex (because then "you" are actually "your sister"), or born with a different genetic makeup, etc. You might as well imagine yourself as someone else in this world, because identity doesn't give you a free ride. Who told you that you're the same person that you were yesterday, incidentally?
Moreover, just because you think you can imagine something doesn't mean that it can happen. There are a lot of ways for something to be impossible, and the deck may not have those five aces in it.
Besides, there are consequences to any proposition. That was Ursula LeGuin's point in The Lathe of Heaven. Sometimes what you think you want has consequences that you don't actually want. In fact, you might scratch that "sometimes" and put in "always." This is a principle that applies even to a single world. You just have to hope that the main consequences of your (always well-intentioned) actions outweigh the secondary consequences, over which you have less control, and certainly have less knowledge.
Ultimately that's why we have ethics, morality, and to a degree, even science. We want to know as much about the consequences of our actions as possible, and we want those consequences to be as good as we can manage. Sometimes we fail. But we should always try, and the trying consists of acting, and not wishing, because wishing doesn't make it so, nor do good intentions.