A man can easily have 300+ kids a year (uhm, well - there are certain biological limitations on the other side - so it'll require choosing the "right time" for women, meaning that up to several K may be required to choose from). And then what? What kind of father will he become? Who will support all that 300+ women during pregnancy and later on? Recently (like in the last century) a mother growing a kid on her own became pretty common and possible - though with some limitations. More that one kid? I've heard of a prostitute who grows 7(!, surely from different fathers, truck drivers) and they are completely "equipped" - clothes, food, toys, etc - so social workers can't do anything about that situation. What's in the head of that kids? No idea. But that situation is an exception and I doubt things will end up well.
Religion does promote responsibility although the form it does that is very indirect. There are societies where a man has multiple wives and there are opposite situations as well - it's all dictated by the life circumstances.
And physiological pleasure and hormones... What will make a man waste his life to support another person or even several? "for free" that is. You can't imagine what could one afford if he had no kids.
Imagine that you don't need to eat or drink to live (that is completely... like you're "solar-powered") - will you waste your time and effort to get food? Maybe you will - if you like the process of eating. Or maybe not - if you don't care or have other tasks. Now substitute the word "food" with "sex" - and you get the picture.