Teenage pregnancy - good or bad?

The CDC report on births garnered attention for showing an increase in teenage pregnancies and births. While this my get headlines, it is not necessarily a bad thing.
The first issue is the arbitrary line drawn. A woman who gives birth the day before her 20th birthday is 'bad'. Wait one more day and the birth would be considered fine. 20 is a rather arbitrary age that does not hold significant meaning of societal responsibility (like 16, 18 or 21), nor does it mark a significant change in human development. Setting a line at 18 or high school graduation may be more appropriate.
Furthermore, the data actual shows a decrease in births to those younger than 15, while the heaviest increase was in the 18-19 group. Perhaps this means a decrease in teen pregnancies is being masked by high-school sweethearts deciding to start their families at a young age.
A better meter would be using unwanted vs. wanted pregnancies. If a couple get married as teenagers and want to have a baby, a pregnancy would be desired. If a 20 year old college student accidentally gets pregnant, that would not be desired. Unwed pregnancy would be a good indicator of 'unwanted' (though the lack of emphasis on marriage in today's culture could mean some of these 'unwed' births were actually desired.) For younger teenagers, unwed births have been going down. For 18 and 19 years olds they have been bouncing around in a narrow range, while for older groups they have been going up.
Another troubling part of the report is the increase in births to older women. These births tend to be much more expensive, requiring significant medical intervention. They also limit the parental involvement in the child's life. A family where each generation gives birth at 19 could easily have 3 generations participating in the raising of a child. A family where each generation gives birth at 39 would be unlikely to get even a second generation to help raising the child.
Younger parents are much more likely to have assistance from grandparents. This allows them to take advantage of child raising experience, while also having the youthful strength needed to care for the child. The child of a 'teenage' birth could actually be much better off than the child of a 'mature' birth.