Why should husband and wife/wives own property jointly?

[gnostic]

And those who don't believe in any religion, and are free to have a sort of marriage with many of the opposite sex, they are not just to their partners as they don't share any immovable property with their partners. In this sense the whole world is of polygamous culture rather than to belong to monogamous culture . Please correct me if I am wrong?

Sorry, but where did you get this crap that non-religious person can have multiple partners at the same time?

No where does atheism, nor agnosticism or whatever non-religious culture dictate that multiple partners are acceptable. I know of no non-religious cultures that find multiple partners in marriage being the norm. If there were multiple partners, it is often extra-marital affairs or they are not married at the same time (either one partner died, or they both get a divorce).

Throughout history, where polygamous marriage have been the acceptable norms, they often come from religious societies, due to some religious customs or other religious-related circumstances. And at least with agnostics (don't know about atheists), we are very big in following customs, but that doesn't mean polygamy is encouraged.

Usually, non-religious people followed the guideline of the law of the land they lived in, and in those countries only monogamous relationships are acceptable. They can have multiple partners, just not at the same time.

Where on earth did you get this silly idea that atheists and agnostics support have many partners as possible? What are your sources?