Nobody could complain if they simply went and made their driver incompatible with the forged chips. If there is no working driver, then the customer would have to complain with the original maker of the hardware and demand a working driver. That's quite within FTDI's rights.
The point is that they attack the firmware of the device involved, which is by no accounts ok anymore. This isn't locking out a competitor, it's destruction of a competitor's hardware. Yes, that competitor didn't act correctly by trying to get a free ride. No doubt about that. By that logic, though, it's just a-ok for any printer maker to trash the printer (e.g. by hosing it with printer ink) should they detect that you use anything but their overpriced original stuff.
We are clearly in agreement here except on a single point: changing the PID is neither attacking the firmware nor damaging the hardware. After a PID change, the hardware (and firmware) is still functional -- as long as either some driver can recognize it or the PID is reset to a valid ID.
It may be that FTDI was unable (or unwilling) to find a way for their driver to stop supporting the counterfeited chips, so they just removed the mask (the PID) on the chip that claimed the counterfeits were genuine. That's not damaging the hardware or the firmware, merely modifying an embedded setting.
All that said, FTDI's actions were not appropriate -- and they will likely end up paying for it in the court of public opinion. However, FTDI's driver did not damage or harm the chips themselves -- and they certainly weren't (as some here have claimed) "bricked."
Regardless of whether they were permanently 'bricked' or not, your initial comment was about 'technologically ignorant users' somehow 'requiring' them to support the fake product - the driver can simply refuse to work with the device.
Now, however, you take that 'technically ignorant user' who went out and bought say 3 x 4GB USB dongles that happened to have fake FTDI chips in them, unaware of that fact of course, who then copies his business critical data, say 3 years worth of work, onto all 3 of them (for safe keeping)... then his machine auto-updates his driver (because, again, he's a technically ignorant user) and suddenly he can't get to his data... in fact, again, technically ignorant, he tries all 3 dongles (if the first one fails, try the backup(s) right?).
Now, he can't even take them to another machine that maybe didn't get the driver update, or a Linux machine without the proprietary FTDI driver... sure, it's 'fixable' by him say paying an IT geek (a non-technically-ignorant person) to reprogram the USB ID, but that's a cost he is incurring because of what FTDI did to his devices. And that isn't to mention that perhaps he needed that data to bid on a potential $million contract with someone, on a deadline that he's now missed because of what FTDI did to 'damage' his devices.
He most certainly, if it can be proven that FTDI is *deliberately* breaking (even temporarily) the devices in question, has a good case for damages from FTDI.