I take the pro side of this topic because while picking and choosing specific genes for your children may seem unethical and greedy, it very well may better the world. First, let's discuss the issue of screening embryos for genetic afllictions and disabilities. To choose whether or not your child is burdened for life with autism or cerebral palsy is an easy decision for most people because of their inherent desire for their children to be happy, and it should be apparent to anyone that this can not harm anything.
As my opponent hasn't demonstrated her ability to 'take me down' I will continue on the subject of prevention rather than modification. Another thing that can be prevented is future illnesses. This happens by inserting genes to tell the immune system how to fight off a specific infection or disease, rather like a vaccine.