It’s not clear to my why you draw parallels with slavery. Spending a massive sum on the days is not an intrinsic prerequisite for marriage, neither is a dowry.
All marriage is, is a formal public oath between two people to spend the rest of their lives together, to look after each other and to share resources.
As an institution, it has many benefits including to the married people’s health. It also negefurs the state in that the mutual commitment to care it tends to reduce healthcare and social costs. So the state may provide some benefits.
The main disadvantage is that she stacks the dishwasher wrong.