Today, abortions are legal because they are an essential human right. Husbands should support their wives' decisions if they want to have an abortion or to continue with a pregnancy. Of course, in the case of a married couple, it is a grave decision which both spouses should consider seriously.
If my wife wanted to get an abortion, I would support her decision. Even if the baby was mine, it's half my fault for not controlling my muscle between my legs in the first place! If the baby belonged to someone else, then my wife and I would have an entirely different conversation than whether or not to abort the pregnancy.