This argument only works under the assumption that we live in a society where divorce does not exist. If a person enters into a marriage without full awareness of what they have committed to and later need to get out of that marriage, they are free to.  Being able to leave a marriage, though, does not make marriage a meaningless charade, as the proposition claims. It is still more difficult to leave a marriage than it is to leave a non-marital committed relationship and so it makes a big difference.