AN ALL-SKY SURVEY IS NOT POSSIBLE AT OPTICAL WAVELENGTHS
Because of the huge number of effective diffraction-limited beams of an optical telescope, it is not practical to pixelate the sky.
This is true. However, there is no law that says that we must be able to undertake an "all-sky" survey in order for any particular approach to SETI to be sensible. It is practical to do both a "targeted search" and an "all-sky" survey at microwaves. It is not practical at optical wavelengths, particularly in the visible regime, for the job would take "for ever and a day".
For political and practical reasons, the "all-sky" survey which was originally part of NASA's Microwave Observing Project (MOP), later renamed the High Resolution Microwave Survey (HRMS), had to be dropped from the later privatized version of the program called Project Phoenix due to the unavailability of NASA's Deep Space Network (DSN). No more than just because an "all-sky" survey cannot now be done as part of Project Phoenix, it doesn't mean that a "targeted search" should not. So with Optical SETI. Optical SETI will just involve a "targeted search" - the same stars under investigation by the Phoenix Project in the microwave spectrum.