"Public charging ports don't have data lines"
Your claim (and that of other's, below) is simply wrong.
Because, any USB charger expected to work with a wide range of devices does in fact have connections to the USB data pins. If they are unconnected, a USB device can draw no more "one unit load" (0.1 A) from the port. If the data lines are actively used, a device can negotiate to 500 mA. Using the USB charging spec, the data pins are shorted together or with a 200 ohm resistor (depends on the version of the spec), and a device it can draw up to 1.5 A. But that's still unlikely to cause problems with other ports.
What is a concern is that there are lots of proprietary extensions beyond the USB spec. Apple and Qualcomm are two big players in that regard, using the data lines to signal the availability of current and/or voltages more that the USB spec itself allows. Modern "universal" charging ports actively use the USB data lines to identify the device type and then negotiate available power. These types of ports are becoming more common everyday.
Even if ports are sufficiently isolated so that one of these "killers" couldn't effect other ports, it's possible that they could damage the port they're plugged into, potentially causing it to deliver voltage damaging to other devices. Even though ESD protection is likely provided (just as it is on a computer's USB port), that's meant to handle only low energy situations (high volt/low amps). These killers are designed to accumulate, then deliver a much greater charge than that.