That's what usually happens, I guess. I remember from an old Steven Pinker book that there is a theory that love is a necessary craziness, because without it we would constantly be looking for better mates (the rational thing to do). That would explain why falling in love makes people do silly things, because they demonstrate "I am crazy, therefore you can trust that I will stay with you".
Yes, a person who approaches matters of the heart with the brain of an economist is generally considered pretty cold-blooded.
Not to say that 'normal' people don't ever do such things, but they are often confined to desperate situations (war zones, disaster zones, economic depression, etc).
