They have no right to use physical violence to express their feelings. Everyone has the right to be safe. If you or someone you know is being beaten, get help. Nobody deserves to be abused. By defending your right to be safe you're letting an abuser know you are serious about their need to change.
Violence can help a relationship.
Abuse is never a sign of love, even if the violence is followed by tender times of making up. Abuse is a sign that the abuser has problems and needs help. The only way to defend yourself if someone insults you is to threaten to beat them up. You can stand up for your rights by being assertive and by being strong enough not to give in to teasing or other forms of insults. You don't have to take away someone else's rights to keep your own.