Can a half brother and sister have a child together?

They "can", but the question needs to be "should they"? The answer is "no". First of all, they are related, so it is most likely illegal. Secondly, the baby would have more of a chance of having birth defects. Also, if the child knows that his parents are brother and sister, it might just have psychological effects on him/her.

AnswerYes! they can. and why shouln't?.

If your fathers are different then you two not related. Since in our patriarchal society the family-line we consider is fathers' side. If your father is same but mothers are different then you are related to one other as half-siblig, and can still marry with your own will. Since you are not fully genetically related. It requires only one thing from your part, that is "a firm decision to go for it", readiness to "face all consequences" and "a strong vow to make it successfull".

Answer from Guduru.Adi

Well if your a christian then you believe that when moses repopulated the earth, they would have undoubtedly have repopulated with inbreds....1st cousins, 2nd cousins, and prob at first close relatives such as half brothers and sisters...The same goes for Adam and Eve in the beginning until now. I know now from going back so far in my family tree, that most everyone is born from an inbred descendant; it's plain fact regardless. In my opinion if your going to be insufferable about social taboo find you something else that makes you happy, instead of destroying the happiness of others. It's just like the christian communities trying to change the laws on gay marriage running overtop of every religion that speaks out..... Our laws say we have the right to religion and not to be imposed with religious prejudice views on them.I can call our country the land of the land of limited oppportunity and freedom. It is so wrong were watching our ally countries like the UK give better freedoms to their people, while our fed. govt. tells us were not giving you those freedoms