As far as worse ideas......well the first AVP would fit into that stat. As far as making it realistic, well you really can go wrong when doing Sci-Fi movies. I mean the realistic part of it anyways. Since it would never happen and never has, you can't compare it's realism to real life events like you could with a Drama. That said, When you have a Sci-Fi movie established with the rules in place, then you can do it wrong. Predators hunt for sport and are "fair" in their practice of killing if you will. Aliens, well they sit at the opposing side of "fair". Not if you change they way each of them are, it better have a great explaination. If not, then you can compare it to the previous films. Namely the originals. The Facehugger in Alien attached to Kane was more than 10 minutes(AVP). Anderson never gave an explanation for the HUGE time difference, let alone a good explanation.