Easily abortion. There is really no contest between a human life be eliminated and gays marrying.
Though opebo would like to cast this as an argument solely rooted in theology, there are many other reasons to care. Emsworth has noted the legal aspects. I would add a scientific basis - we have a standard recognized in 50 states that heart beat and brain activity in a human constitute life for the purpose of determining death. A consistent scientific definition would apply to the unborn as well.
Exactly, Judiasm (my religion) actually supports abortion.
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