People take taxis when they are drunk. People are more likely to engage in sex while drunk. People take taxis when they want a degree of privacy as they travel, as opposed to busses. People are more likely to have sex when in a semi-private space. A taxi provides a degree of physical security, a barrier between you and the mob. Why is this a surprise? In SF I expect that some taxi startup will soon target this market directly.
I don't take taxi for the privacy but because public transports suck in Paris at night. Past 2AM the metro doesn't works, the train to Versailles (next to where I live) doesn't work, the bus to my city also doesn't works.
The second biggest issue when taking public transport while drunk, is sleeping and missing your stop.
