In modern civilization man thinks that he lives for pleasure, so the woman for him - it is an object of pleasure, and children, of course, for a man - a burden and austerity, so the man asks - why should I have children, if I can just walk with women and establish a relationship with them, and if they have children, you can simply give them up and take that is not mine. This is a sinful life, generating a bunch of suffering, because when a man is so configured - it will never develop as a reasonable person, because a sign of rationality - is taking responsibility.
Responsibility - is suffering, ie a person can not be responsible if it does not suffer. For a man, it is children - ie this load: men need to work harder, take more responsibility, more spiritual forces to invest, but it just means that it is developing as a person becomes more intelligent, more mature from such activities. And then he becomes happier.
If a man thinks that his life is only for pleasure, and therefore it is necessary to meet women, use them and do not have children, then that means degradation.
"Why do I need to start a family?" - Could be the next question, because why the family, if there are children in it, you can just walk. This means degraded life. Therefore, people do not marry legally - they do not want to take responsibility for any husband or wife for, not for children. They just want to enjoy each other, meaning miserable existence, which leads to only one suffering, because the more a person enjoys, the sillier it gets. Reasonable man rises only from performing his duty, responsibility, obligations, oaths, promises, and that this life leads to rationality and happiness, and irresponsible life aimed at pleasure - leads to only one suffering.