Why does Theseus tell Hermia to come to terms with her father's choice of husband for her in A MidSummer Night's Dream?

In A Midsummer's Night Dream, Theseus
tells Hermia that she needs to obey her father, because in that time in Athens,
daughters were the property of their fathers until they married, and then they became
the property of their husbands.  It was the law of Athens that she must obey
Egeus.

Theseus also points out that Demetrius is a fine
choice for husband, as he is well-bred, well respected, and was her father's choice for
her. She, however, counters that she does not love Demetrius and as a young girl she
wants to marry for love, not money.

Theseus did, however,
give her some options. If she chose to disobey her father and the law of the land, she
could join a convent and shun men the rest of her life, be banished from her homeland
forever, or be put to death. None of these options are particularly good ones, so she
had strong motivation to "make the right choice."