Well there are many pros and cons to this question.

If you legalize it, you can be sure that morality of the public will take a great turn, from conservative to liberal. Although you will have lesser rate in:

Baby dumping cases
Young couple divorce cases
forced marriage cases
etc

You will risk more of :

STD epidemic
HIV Spreading faster and at a higher rate
Morale of the society dropping
Teen being more irresponsible
and ofc, more innocent lives being taken away.

So, if you ask me. No it shouldnt be legalized. If one is thinking about having physical intimate intercourse then one should be mature enough to understand the consequences . There is no reason to say that you did it and didnt thought about what will happen next. Even the best reason is not the best reason at all to take an innocent life away, what more it is an excuse?