Although everyone has his or her own opinion of adoption, there is no right or wrong reason to adopt. Generally speaking, adopters choose to adopt because of infertility or a desire to raise a child that may not have otherwise had the chance at a supportive lifestyle.
For some adopters, it makes more sense to adopt a child in need than to bring another into the world. Similarly, some adults don't have time to raise a child from infancy and find that an older child is a better fit. Maybe there are medical reasons, perhaps there's a genetic disease that someone doesn't wish to pass on. Or maybe a couple is infertile, gay, or past an age to conceive a child. Maybe an adopter is single and looking to raise a child alone. Whatever reason for adoption that brings you to the community may even change as you explore the different adoption options out there.
Reasons for adopting do not always align with the reasons a couple want to have a child. All parents want a child to love and raise. A couple may want a biological child because they feel they're in control and responsible for the child's natural talent and behavior. However, this is as much a fallacy of wishful thinking as adopters looking for the "perfect" child. The reasons for adoption are as varied as the families created by the process. The only right answer is the one that is right to you.