The reason I give my family is one that basically sums it all up.
I feel that they don't teach what they should teach, and do teach what I don't want taught.
One thing that you always hear is how homeschool children are deprived socially. Well, that happens to be one of the reasons we homeschool. There are certain "social skills" that I don't want my elementary, middle school, or high schooler learning. I went to school in a good suburban school district and I remember.
Also, my mom works in the school systems. Sometimes I wish I had a recording of some of her stories so that when she asks why we homeschool I could just play back some of the events of her students/teachers/classes.
I like being able to take a break from school when we need it. Not when the calander says we should. (ex: birth of a child, moving, emergancies, etc)
I like that my children can learn at their own pace.
I also like being able to adjust the day as you desire.
Being able to use the bathroom or get a drink or snack when ever you need to is a small benefit.