I'm really shocked that married couples live that way. I've been married over 30 years and have no idea about the concept of "my' money or "her" money. Whatever we earn gets dumped into joint accounts and we pay the bills together. If enough if left over, we go out to eat or take a vacation. It's always been that way and I know no other way.
I can see a lot of arguments ensuing over trying to keep the money separate in a marriage.
That's because you're both trustworthy. What you have is called a good marriage. :-)
Unfortunately, not everyone is trustworthy. One unscrupulous spouse can clean out a joint account and run off with the money. It happens all the time.