First of all, it's a great idea. 
Major airports get named after people who have had a major impact on society (LaGuardia, Kennedy) or heros (Lt. Commander Edward O'Hare ) and Harvey Milk was both. SFO is the gateway to the United States for millions of travelers, much as Kennedy is on the East Coast, and the idea that all of them would be potentially exposed to Milk's life and legacy is wonderful.
Sup. Scott Wiener supports the idea, but says it will "spark a robust debate" about other people who have contributed to San Francisco, and I've heard the names Dianne Feinstein and Willie Brown mentioned. Both were bad mayors, both sold out the city to developers, both would be an embarassment -- but that's not the point. There are plenty of politicians like Feinstein and Brown in the world; there was only one Harvey Milk.
Thanks to Sup. Campos for the idea. I suspect it will get about 70 percent of the vote.