The question is in debate for long with many people favoring the birth control for autistic teens while others saying it is not appropriate. But the question is like asking like if a person be denied life just because he or she has some defect. Just because autism brings in several complexities into a person’s life does not mean that he or she should be denied the rights of reproduction.
The other interlinked question is whether the normal teens should be allowed to have sex? It is the duty of the parents to educate the teens about the meaning of sex and the results etc that include birth control, safety precautions etc. The parents cannot control the life of teens though they can educate them. If the teens understand, they can wait or have safer sex.
Coming back to autistic teens, same principle should be applicable here too. As a parent, you will teach the autistic child everything as you did before. So why will you not explain to him or her, what sex means. If the person is able to comprehend, this means he or she can take care of the issue. There is no use debating this.