Dozens of people protested Saturday in Chino Hills against a neighborhood home that they claim has been illegally operating as a birthing center where pregnant Chinese women fly in to give birth so their babies will be American citizens. . . . Southern California has become a hub of so-called birthing tourism. It is not illegal for pregnant women to travel to the U.S. to give birth. Birthing centers advertise in wealthier Chinese cities, where some women can afford the thousands necessary to make the trip to America for a few months.